as both you and i have said, the GPU will become more important as apple continues to incorporate it into the core functions of the OS. the 5200 has no problems handling expose, core image, etc. so i don't see your rational for having to upgrade sooner, your 15" will need to be upgraded just as soon to take advantage of the next OS's features (10.5?) such as 64 bit etc. you say WHEN adobe integrates CoreImage? IF they integrate core image that is...don't forget they make software for Windows as well, and CoreImage isn't a windows technology. Not to mention Adobe isn't exactly a huge supporter of Apple since Apple has begun killing several aspects of their business, and even if they do, the 5200 supports CoreImage, so this is a moot point...CoreImage from the Tiger demo runs fine on my 12" currently, you can only assume when it's officially released it will be further optimized. Perhaps the 9700 will "fare better" but it's not as if the 5200 will run CoreImage choppily, when Apple states the card is supported, they tend to mean it can run the features AS INTENDED, not half assed. If you recall you can use hacks to aquire video mirroring and Expose on unsupported graphics cards, but HERE it runs choppily, because they are not supported (doesn't mean they AREN'T CAPABLE, they just aren't capable of running it AS INTENDED without stuttering and dropping frames).
Yes Macs can RUN games, but nowhere near on par with a PC, it's slowly getting better, but we're talking slow like glass (which yes...is a "liquid"

). I wish it weren't true since i too am a gaming nerd/mac fan, and i'd love to rock out to some Halo (2?) on my 17" lcd, but unfortunately I'm forced to use an xbox to get "decent" gaming (the library is horrible...i own two decent games, halo and ninja gaiden). Alot of it has to do with M$ and DirectX 9 support, because Mac's are excellent at floating point calculations...which is what games use heavily, so a Mac SHOULD crush a PC in a perfect world.
I'm glad you enjoy your 15" it's an excellent computer, but it's not exactly a true portable in my opinion. I'm already cramped as it is on a train with my 12", the 15" wouldn't even fit (the monitor would be pressed up against the seat in front of me) and the 17...well forget about it. I do agree the 15" screen is GORGEOUS (wide aspect ratio) but I travel alot and really appreciate the small size. When i'm not traveling I connect to an external monitor because I have to agree that 1024x768 is FAR TOO SMALL to do serious design work. It does however make an excellent palette screen

. For web browsing, email, chat, video, etc. it's perfect, but when I have Director open with the stage, score, cast, etc. it can get ugly really quick. the 12" is not what i'd consider a true DESKTOP replacement (meaning no external monitor, keyboard, or mouse) but it makes an excellent slim CPU when i'm at my desk and can hook up to my LCD, Apple keyboard and bluetooth mouse.
To answer Chips question again...both graphics cards support CoreImage and all the features of the current OS (10.3) as well as Tiger (10.4). If you really want a 12" DO NOT FRET OVER THE 5200fx, many people like to crap on it cuz it's Nvidia or its "only" 64mb or whatever, the truth of the matter is it handles all my tasks with aplomb, you'd see a larger speed increase by swapping the hard drive for a mobile 7200rpm. Nvidia also tends to have better OpenGL support, which is what Mac OS X uses, so i'll let you draw your conclusions from that.
i doubt you'll notice the difference between the 12" and 15" graphic cards aside from HEAVILY GPU TAXING TASKS (no expose does not heavily tax the GPU, i'm talking about full screen visuals on an external monitor with anti aliasing where you need above 30fps or it'll look slow) CoreImage isn't exactly GPU taxing either, it requires the latest graphics technology (pixel level shaders) which is why you need a current card.
sry if i came off like a @$$ but i think people give the 5200 alot more flak then it deserves.