Don't diss the 15"
Seems this is a 12" love-in, so I guess I should play Devil's advocate.
Don't get me wrong - I owned two 12"s and loved them too - but as far as portability goes the 15" is extremely roadworthy. It may feel more like carrying a folder than a novel, but for the power and screen space it packs, it is remarkably compact.
And that being the point - compared to the 12", the desktop is luxurious. You can actually pages/windows side by side rather than cramming it all in. And if you're a fan of having all your apps conveniently located, it allows you to have a much bigger (longer/larger) dock (yes, that's dOck
). Power-wise, whilst the 12" has improved substantially in this third revision, the 15" now holds the mantle of Apple's most powerful processor. If as much power as possible is important to you, then the 5400 hard drive combined with the 128 VRAM and the 1.5Ghz processor (and nearly double the expandible RAM of the 12") sets it right apart from the 12". It also has a PCMCIA slot (which may not be of as much use nowadays, but who knows) and FW800 (which definitely will be), and the awesome backlit keyboard. Having said that, I hate to say I barely use this machine to its limits. But at least when I do, it will totally rip.
Another improtant factor is the battery life - the rev C 12" seems pretty good, getting 4 to 4.5 hours for many people. Since I received my 15" I have had XCharge on continuously, and have put a decent power management strategy in place (screen brightness lower for better lit areas, display and hard drive sleeps within 3 and 5 minutes, bluetooth off but Airport on) that gives me 3.5 hours regularly. I find this is more than enough for me, and even if it weren't, the extra hour would probably not make that much difference - others may find they need to squeeze every minute they can out of the battery, so that's somethign else to consider (though you could simply buy a spare).
But that's just me - given your circumstances (since you feel that you need to justify the 15" to yourself), you should probably just get the 12". The danger is you may pine for the 15" anyway, so have a long hard think about whether you can afford it and whether the usability advantages of it outweigh the small portability advantage of the 12".
I tell you, it's a tough dilemma - no right choice, just the right choice for you (if there's even that!).
Good luck - let us know how you go.
