Keep in mind it's actually an 8gb limit; 4gb sticks just aren't on the market yet. But if you're planning to futureproof via memory, the extra gigpspace may come in handy.
Actually, the GM965 chipset only supports 4 GB (page 12, section 1.1.2.) This is regardless of individual module size. The desktop G965 supports 8 GB, but not the mobile.
There are enough "plusses" for the 2.2 that make it worth more than the 2.16, although I think that they have all been mentioned, it is the faster processor, up to 4GB or RAM, a better graphics chip, and more controls on the keyboard.
Haha, that's partly my bad, and partly yours. Seeing "haven't", I thought you had meant "I" instead of "He". Just the wrong usage of "haven't". Should have been "hasn't".
But ya... HE should try it. It's a great OS, especially on the MacBook. Spaces is a life saver with a 13" screen.