Petteri Sulonen is right on the money:
I used to participate on Photosig, but I learned to hate it. It exerts a huge pressure of blandification — shooting for the lowest common denominator. Flowers, bug macros, anal-retentive “figure studies,” golden-hour landscapes, pouty soft-focus “glamour” ladies, you name it — every photographic cliché ever invented is celebrated there on a daily basis.
My advice would be: steer clear of Photosig like the plague, if you want to retain a modicum of individuality in your photography. If you’re strong enough to resist the temptation of starting to shoot for thumbs-up, you don’t need the affirmation anyway — and if you’re not, you risk your artistic integrity and individuality (yes, you do have it).
When I found myself shooting a sunset by the sea and thinking “this’ll score me a few thumbs,” I quit cold turkey.
See his five-page (it’s not that long, actually) analysis on why sites like photoSIG doesn’t do good to your photography, and why you should use Flickr instead.
Flickr doesn’t actually get you any better critiques than photoSIG or any other photo-sharing sites or forums—unless of course if you consider one-liners or those it’s-not-sharp-enough comments useful—but at least the networking aspect of Flickr is tremendously useful for anyone wishing to make a break into photography.