I may be in the market for a new computer but may not want to wait until an un-specified date. Considering the massive amount of sales that Apple is conducting, it seems to me that it may be a smart move for them to provide a less-expensive Tiger for those who recently bought an Apple. After all, they will see a surge in purchases after it comes out for all of those who were paitent unlike me.
In the past Apple's Up-to-Date programs have only covered computers purchased after the official product announcement. If you are hoping to get a discount on Tiger, you'd better wait until at least then. If sources are correct though it looks like it might be only a month from today that Tiger hits the streets. I'd wait until at least April to order.
According to the past, if you order the computer on or after the date of the announcement of Tiger, you'll get a discounted price on the OS. If you order before that, you have to pay full price for the OS. Rumors are starting to suggest that the announcement will be made around the beginning of April. Wait two weeks or so, not a big deal.