I've experienced this form of freezing as well on my base 15" Pre-SR MBP. Symptoms are:
- Computer is non-responsive except the mouse cursor
- The mouse cursor moves but can't do anything else (click, start apps, etc).
- The computer has not kernel panicked.
- I can't reproduce it
- It isn't RAM (I've tried 4 different sticks of 1gb DDR2)
Its not in the country right now but when it comes back on Saturday, I'll be bringing it back to the Apple store to get it checked out. I'll keep you posted on the results.
If you're within the 14 days, I HIGHLY recommend you replace it NOW.
There's also this
thread where are lot of us that are experiencing freezing have posted our experiences.
Good luck, its annoying and for me, it didn't start happening until 4 - 6 months after I got the laptop.