The problems kicked off this morning when Amazon started sending emails to select Kindle owners, alerting them to a free trial of “The Kindle Compass.”

In the email, Amazon failed to explain what “The Kindle Compass” was, and worse, implied that customers would be charged for it going forward.

An Amazon spokesperson said a second letter has been sent this evening, explaining that “The Kindle Compass” is a pilot project, and apologizing for any confusion over the price. “We built it to always be free for customers, and you will never be charged for it,” the company told its customers.

Still, the response comes hours after much of the damage had already been done.

Angry customers flooded Kindle forums, posting more than 100 complaints to topics called “Where is Kindle Compass Magazine?” and “Auto-Subscription to the Kindle Compass??”

The confusion was understandable.

In the original message, Amazon misled consumers about the terms: “If you enjoy your free trial, do nothing and your subscription will automatically continue at the monthly subscription rate.”

However, no rate was ever mentioned.

Even worse, those who contacted Amazon customer service said the reps weren’t familiar with the publication, so the best they could do was help them to unsubscribe to ensure they would not be charged. At this point, people are still confused as to what “The Kindle Compass” is all about.

A spokesperson did not return emails asking for more clarity on what the publication is, and it’s unclear how many customers were affected (not all Kindle owners received the email).

In the forums, the complaints centered on two concerns: That Amazon would sign them up for something they did not knowingly subscribe to, and that they may be charged for it.

One consumer, who used the name “Susabelle”, wrote: “I am absolutely APPALLED. Amazon, you should be completely ashamed of yourself!! An auto-subscription to a publication I’ve NEVER heard of, that you will be auto-billing me for after 14 days? HAVE YOU LOST YOUR MIND??”

Here is the apology Amazon sent to consumers this evening:

This morning we sent you an email regarding The Kindle Compass, a new free publication built by the Kindle editorial team that we’re piloting to a small number of Kindle customers.

This email incorrectly referred to The Kindle Compass as a subscription with a free trial. We built it to always be free for customers, and you will never be charged for it. We apologize for any confusion.

If you wish to unsubscribe from the pilot for The Kindle Compass you can do so from a link in the last section of the magazine, or from the Manage Your Kindle Subscriptions page at www.amazon.com/manageyourkindlesubscriptions.

Spotify, the much hyped service that has yet to appear in the U.S., is a mobile play. Rival MOG says it will have a mobile subscription offering in the near future as well. But the new mobile product from RealNetworks’s (RNWK) service, Rhapsody, has actually been up and running for a little more than a month, and the company says results are encouraging: Real says that more than 500,000 people have downloaded its app for Apple’s (AAPL) iPhone.

The problem: This stat alone doesn’t mean much. You can only get streaming music through the Real app if you’re already paying the company $14.99 a month for its “Rhapsody to Go” service.

So how many app users are paying customers? And more important, how many of them became paying customers because of the app?

I’ve asked Real for comment, but I don’t expect one, since the company has typically been close-mouthed about this stuff. But I’m told that Real has about 700,000 to 800,000 paying Rhapsody customers overall. So it’s possible that almost all of the app downloaders are already paying customers and that the app is just a nice bonus.

Did anyone out there actually start subscribing to Rhapsody because of the iPhone app? Let me know via email or in comments below.

UPDATE: Real, to its credit, isn’t making too much of the numbers itself. From spokesman Bill Hankes:

Although we are pleased to see excitement and interest in the Rhapsody iPhone app, it is too early to tell how this will translate into subscriber numbers since we suspect many of the people who downloaded the app are current subscribers already or are trying Rhapsody for the first time with the seven-day free trial.

Here are a few questions about computers I’ve received recently from people like you, and my answers. I have edited and restated the questions a bit, for readability.

Best Buy is offering a free upgrade to Windows 7 if you purchase a machine today that has Vista. Is it better to wait to buy after the release of Windows 7?

A: I’d say so. If you buy a Vista machine now, you’ll likely have to spend at least some time and effort upgrading, and you may run into at least minor issues, which is something that sometimes happens even with straightforward upgrades. Since PCs preloaded with Windows 7 are only two weeks away, it’s worth the wait, unless you are in dire need of a new PC right away.

With the end of Microsoft Money, are there any good alternatives to Quicken? I tried Quicken Online, but it is just too limited.

A: I haven’t reviewed it, but a program called Moneydance might be worth checking out. It runs on Windows, Mac and Linux, and claims to import data from Money and Quicken. Moneydance costs $40, but there’s a free trial. Information and downloads are is at moneydance.com.

I read that upgrading to Windows 7 deactivates the license key for any prior version of Windows, ruling out any chance of reversing the upgrade if it doesn’t work out for some reason.Is this true? If I am going to take the plunge into Windows 7, I want to make sure I can always go back if I’m unhappy.

A: Microsoft says that’s false. The company emailed me to say: “The upgrade process does not deactivate the product key for the previous version of Windows. If you need to uninstall Windows 7 and go back to your previous version of Windows, you can activate it using the original product key.”

You can find Mossberg’s Mailbox and my other columns at http://walt.allthingsd.com.