It’s too early to know for sure; there are two days left for last-minute packages to be delivered, wrapped and placed under the tree in time.

So, while it’s hard to say whether there will be any widespread panic come Sunday, there are some early indicators that the system is reaching capacity.

In perhaps the biggest demonstration of holiday stress, a FedEx delivery driver was caught on camera tossing a box containing a new computer monitor over a customer’s fence. The owner claims he or she was at home at the time, with the front door wide open. After nearly five million people watched the security footage on YouTube, FedEx responded by posting an apology on YouTube. (Only 193,000 people have watched that.)

Then there are the canceled orders at Best Buy, which ran out of heavily discounted merchandise and was forced to void some orders that consumers had placed last month. A few more reports have surfaced from other retailers, such as Sears, which was failing to keep up with orders that were placed online for in-store pickup.

But perhaps this sort of thing is to be expected when you see 15 percent year-over-year online growth in online shopping.

ComScore reports that e-commerce spending for the first 48 days of the holiday season has reached $32 billion, jumping 15 percent over last year. Last week alone, ComScores said, four individual days surpassed the $1 billion mark, to help set a weekly record of $6.3 billion.

On a positive note, retailers’ Web sites have been able to keep up with the demand. Compuware, which has been monitoring the Web and mobile performance of the top 50 retailers, reports that there have been no prolonged site crashes.

At this point, most online purchases won’t get to people in time for Christmas, although Amazon is offering some expedited shipping options for consumers in some markets as late as Saturday.

Besides stress on the retailers, one other choke point in the system has been delivery.

This week will be the busiest week of the year for UPS, which estimates that it will deliver more than 120 million packages worldwide. In particular, it was anticipating that today would be its busiest day, with more than 26 million packages shipped — which breaks down to about almost 300 a second.

UPS’s close competitor, FedEx, previously predicted that Dec. 12 would be the busiest day in its nearly 40-year history. The company was forecasted to ship more than 17 million orders that Monday, which was double its daily average volume.

Dear Apple Store Customer,

You recently received a Shipment Notification email from Apple advising you that your iPhone has shipped.

This email is to confirm that your delivery will occur on June 23rd. Although Apple and FedEx tracking information may currently indicate a later date, you can check the FedEx website the morning of the June 23rd to track your package to your doorstep.

In the event that you will not be available to accept delivery on June 23rd, it may be more convenient to use our pre-sign delivery option by visiting our Order Status website at http://www.apple.com/orderstatus.

Sincerely,

The Apple Store Team

The reason for the change in delivery date isn’t clear, though it might be that Apple is hoping to protect its servers from meltdown by staggering initial iPhone activations over two days.

Read Walt Mossberg’s iPhone 4 Review »

As of this writing, Apple (AAPL) continues to accept preorders through its online store with a promise of Friday delivery, though oddly, InformationWeek claims the company and its exclusive carrier partner, AT&T (T), have both already sold out of preorder units.