I hate Sony Memory Stick :|
That being said, I have DSC-F707 and DSC-S75.
Battery life is more than excellent on F707, even better onf F717 according to Phil.
I've been to volleyball tourney with F707 and manage to fill 3 x 128MB in 2 hours with more than 1/3 battery life to spare and I use LCD all the time.
I've never use a spare battery yet.
A 128MB MS can store about 55-ish pictures
Noise Reduction is not use to reduce noise on ISO settings per se but mostly on low shutter speed.
I think it 1/30 sec or lower then NR kick in.
NR makes your night shot look pretty.
one of the reason why F707/F717 can focus fast and great low light performer is the lens.
f2.0 - f2.4 is a fast lens, only Oly C-5050 f1.8 is faster in 5MP DC.
You will appreciate fast lens when you shoot a lot of picture in less than ideal lighting.
Video on F717 is MPEG HQX - 320 x 240, 16 fps, no limit, including audio
(5 min 54 sec on a 128 MB Memory Stick)
As for video quality on DC, they are ok, I'm not a fans of camcorder so I think video with DC is good enough.
IMHO, Canon S50 can't compare to either F717 or G3.
The lens is too small and slow, and Canon push the imaging CCD too much on S50 that the noise is evident.
G3 OTOH is an excellent camera. Can't compare to F717 in resolution area but other than that pretty much equal or better.
Canon have much better control choices and can shoot RAW.
Color is less agressive compare to Sony's, more natural looking.
Using CF is also a huge plus
Pros on F717
Fast Lens, 5X Zoom, Long battery life, top notch resolution
cons on F717
color can be exagerated at times, sucky MS, no B&W effect, large.
Pros on G3
Use CF, all the control/settings that u can think off, more natural color, swivel LCD
Cons on G3
not 5MP ? not much cons really. Only $100 less (MSRP) than F717