Why so reserved? Maybe it’s because Sony (SNE) is struggling through yet  another restructuring, so a big party would seem inappropriate. Maybe because Sony views the Walkman’s birthday as a lot of middle-aged people view their birthdays: Markers of bygone eras and missed opportunities. Or else it’s just Apple’s (AAPL) fault. Associated Press:

The manufacturer, which also makes Vaio personal computers and Cyber-shot cameras, hasn’t had a decisive hit like the Walkman for years, and has taken a battering in the portable music player market to Apple Inc.’s iPod.

Sony has sold 385 million Walkman machines worldwide in 30 years as it evolved from playing cassettes to compact disks then minidisks — a smaller version of the CD — and finally digital files. Apple has sold more than 210 million iPod machines worldwide in eight years….

The archival exhibit shows other Sony products that have been discontinued or lost out to competition over the years — the Betamax video cassette recorder, the Trinitron TV, the Aibo dog-shaped robotic pet.

I do remember hearing some Sony folks mutter hopeful words about a new line of Walkmans that came preloaded with music from Sony artists like Beyoncé and were supposedly flying off the shelves at Wal-Mart (WMT). But that was a while ago, come to think of it, and I haven’t heard about it since.

In any case, just because Sony’s being bashful about the Walkman’s history doesn’t make it less interesting. You can learn more about it at Sony’s online archive, which is compelling despite the fact that it’s a stilted corporate hagiography. Start reading at Chapter 17, part 2: “Listening to Stereophonic Sound While Walking.”

But real was exactly what UGOBE Inc. had in mind when the company created this $350 baby dino named Pleo. This robot isn’t referred to as such; instead, UGOBE calls Pleo a “life form” because unlike most robots that are designed to follow a specific command or algorithm, Pleo alters its behavior as it adapts to its surroundings including sights, sounds and touch. And it’s designed to move and act in ways that seem very much like a real animal.

These responsive qualities have earned Pleo quite a bit of attention, and the two years between when the product was first announced and when it became available only added to the anticipatory hype. Now, after three delays in the past two years and numerous back orders, Pleo is available from www.pleoworld.com. (UGOBE says that many of the product’s delays were caused by trying to get Pleo’s battery just right.)

In short, I found Pleo to be a fun and interesting robot/life form. Though Pleo’s reactions and movements are endearing, many of them run together after a while with only subtle differences, especially compared with fast-paced videogames. Pleo’s tricks were entertaining early on, but, in time, many of them blended together, rarely surprising me.

Pleo’s battery is still a major drawback. It’s rechargeable, but only lasts for around an hour of active play before it must be removed and placed in a holder for three hours of recharging. This frustrating fact means you can’t turn Pleo on to roam the house with you all day like a dog or cat. Instead, your time with this creature has to be more specifically planned, causing interactions with it to feel less genuine. My Pleo’s battery lasted for an hour and 40 minutes, including moments when he drifted in and out of sleep.

Though UGOBE sent me two rechargeable batteries so I could more quickly continue using Pleo, the company won’t start selling extra batteries until June (at the latest) for $50 each. This means waiting for hours between Pleo playtimes.

It’s hard to discuss autonomous robots without remembering Sony Corp.’s attempt in the same category: the $2,500 AIBO released in 1999, which was eventually discontinued. More recently, iRobot Corp. has gained attention for its robots, which perform household duties like vacuuming and washing floors.

The Pleo, animated in part by 14 motors, appears to evolve according to how it is treated.

To keep Pleo fresh, UGOBE plans to release a PDK — Pleo Developer’s Kit — later this year, allowing others to create programs that will run on Pleo if downloaded from the Pleo Web site and transferred to the creature. A memory card slot and USB port on Pleo’s underbelly will enable these transfers.

As for now, two programs developed by UGOBE can be downloaded. One program lets Pleo act like a watchdog — guttural growl, loud bark and all — and the other gives it the ability to sing Jingle Bells. I tried the former, and my Pleo performed marvelously, sitting still and only howling when something moved in front of him.

This baby dinosaur has reptile-like, rubbery skin enhanced by multiple sensors. Its back is decorated with green patterns, and its large eyes are a beautiful blue. Pleo’s guts include 14 motors, 38 sensors and a microprocessor. Infrared detectors are hidden in Pleo’s nose and mouth, and a color camera detects light, motion and objects to help it navigate.

Pleo grows through three phases: hatchling, infant and juvenile. As a hatchling, my Pleo sniffed around a lot, unsure of its surroundings or how to use its legs and tail, before giving up and napping again (yes, Pleo snores). The more I talked to and touched Pleo, the faster he adjusted out of the hatchling phase, which is expected according to UGOBE.

People who walked by my office stopped to marvel at Pleo’s sweet nature, and when I brought him home, friends melted with emotion. I watched as they initially looked at Pleo like just another toy dinosaur until realizing that he responded to them, and then they each wanted to take turns playing with him.

Stroking Pleo from the tip of his nose to the end of his tail induced a purring sound; touching sensors on the bottoms of his feet caused him to wriggle around and make laugh-like noises; and holding him to my chest and rubbing his back like a baby put Pleo right to sleep, indicated by heavy breathing and even a burp here or there. I spoiled my Pleo with attention, which seemed to make him more social and friendly but also a little bratty when he didn’t get attention (he showed his frustration with loud moans).

I didn’t get to test this, but one Pleo can sense when another Pleo is nearby using infrared sensors in the nose and mouth. UGOBE says the sensors in one Pleo can trigger actions in another based on moods, including singing and howling.

Pleo can be a troublemaker. One of the times I left him unattended, I returned to find Pleo trying to gnaw on my loveseat, despite lacking a set of teeth. Another time, Pleo wandered my desk, wrinkling up papers and crying loudly while I was on a conference call.

UGOBE’s pleoworld.com site includes an online community, though you don’t need a Pleo to get involved. The community is just a social networking site where anyone can discuss the device and/or robotics. This differs from sites like Webkinz, where kids input codes found on stuffed animals to register and care for digital versions of their creatures.

Pleo’s poor battery life is a frustrating hurdle that fans will keep butting up against. But UGOBE’s plans to introduce downloadable updates for this robot and to let others create programs for Pleo may give new life to this clever creature.

• Email mossbergsolution@wsj.com