1. small size - my main interest is shooting people, and I don't want people to be freighted by big camera;
GF1 or EP1/2/l1 are the smallest of the bunch - further to this the Oly kit zoom is the smallest when colapsed... just. - I assume a Rebel Ti is too much camera for your likeing? As like prev poster said, this covers most of your needs very well, but looks like a "proper camera" Ahem.... cough* cough*
All the m4/3 cams are quick and responsive - but auto focus is noticably faster on the panasonics....
3. an optical view finder will be nice;
Thats a good reason you might want to look at the canon Ti thing....
But you could get the EP1 and kit 17mm pancake with a OVF all be it not through the lens... bit crap realy.... not what your after I'm shaw - just cut out a square of plastic, bluetack it to the top and
bang you have one!
4. good high ISO (low light) performance;
GH1 is the best m4/3 buy say (for arguments sake) a stop...
I personaly am without issue using my EP1 up to 800iso, but will be ok with using 1600iso but I won't go higher... with the GH1 I feel I would use 3200 as my top end - images are not perfict but still good at 3200 on the GH1
5. good video function - I am a fan of classic music and ballet and will film lots of them, very often, they are indoors;
Like has been said - Definatly the GH1 will be the best for video - arguably better than any other SLR type cam in existance.
But all the others do make very good quality video. The EP1 has a resnoable mic too - good sound quality... can't talk for any other m4/3 But the GH1 can also have proper external mic accesory...
EP1 has a 7min time limmit to its video clips, but has digital stabalization. Panasonic will only have lens stabalization (I say only, because it will not be there when adapting old MF lenses form other systems, but lens will be better than digital - digital in this case crops/zooms the image slightly to alow for shifting compensation)...
Panasonics Have AVDHC as well as MJPEG - good to have as an option, but not essential.
Herd the strap luggs can come off old GH1s (fixed now) but apart from that all are built very well... As good as any other... even the epl1 is not gonna fall apart....
What I don't care are:
1. ability to shoot raw;
2. flash;
3. macro.
All shoot RAW
No flash on ep1/2 - all others have one..
EP kit zoom trys admrably when goign for macro - but is not substitute...