It seam that the new 2011 MacBook Pro 15" & 17" models "freezes or becomes unresponsive to input when under heavy load" in fact the issue is so widespread and troublesome that an entire 'wiki' has been made for it at http://mbp-freeze.wikispaces.com/
The details of the issue is not what I want to discus here, what I want to talk about is the danger of buying new tech immediately. Apple, Canon, Nikon, Adobe and every other company on earth make a huge deal about getting you revved up to buy immediately each time they come out with a new product. Personally I dread it because when you work on set everything needs to work and work flawlessly! This is not to say that I don't like the new stuff, I just don't go out and buy it immediately, I wait to see what issues come out on the blogs, and there are almost always some issues. "Freezes or becomes unresponsive to input when under heavy load" I would be devastated if I grabbed a new MBP and jumped on a plane for say Patagonia for a 2 week long shoot only to find that every time I try and process or open a large file my computer crashes!
Personally I really like to buy refurbished Apple Computers when I can because they go threw them and test them more extensively than a just off the assembly line computer, not to mention you can save some CA$H (around $800 on the MBP above) I have not had any issues with a referb yet! I have had and dealt with many issues on new computers and they normally come to the surface pretty quick.