I don't get why anyone is saying this is better than Flickr. I suppose it has to do with how you use each site. Flickr has so much more integration with so many more platforms. For the price and amount of useful features you get with Flickr... for the price, I think they can't be beat.
500px is interesting so far. Not quite sure what I think about it. Sort of feels like a giant photographers club. I don't usually hang out with typical photographers and don't really care about conversations that have to do with how many megapixels their camera has or how much their lenses cost. Or, what new HDR technique they're trying out. Don't get me started on HDR. Talk about overdone!
So far, although I think 500px is far too overrun with girly photos, insect macros, over-processed landscapes and cliche fashion shots, I think it's worth keeping an eye on.
I like that 500px seems to be evolving and shifting to keep the focus on photography, but the audience here seems to be mostly if not only photographers. It seems like a mix of the pixelpeeping shutterbugs from dpreview, mixed with the traditional clique from photo.net, stylized girly images from altphoto, with a mix-mash of Flickr users thrown in as well.
All in all, I LOVE the interface and overall layout. I just wish the audience stretched out beyond just photographers and the typical cliche images. Don't get me wrong, many of the images here are stellar for sure. Even many of the nudes and girly photos are nicely done. But at the end of the day, It just seems like the overabundance of one style over another is getting boring.
That being said, there's enough here at the foundation that keeps me interested a bit longer. Especially to see how 500px evolves and innovates this further. It's a different animal from Flickr for sure, but for image management, integration, publishing tools, etc. it's hard to beat Flickr for the low cost.