I'm kind of in the same boat as Jan - I pretty much use flickr as an avenue to share photos on forums. I liked the simple format of the old style but the new style isn't all that bad. I don't really follow people too often nor to I update it very often.

I've been on 500px for a while now and I must say that the standard of photos there far exceeds the standard you see on flickr in general. I also find it easier to find photos of a particular genre/subject etc on 500px. I like it but similarly to flickr I get sick of the copy and pasted "Nice pic, voted and faved. Please vote for my latest work also" comments. I generally ignore those.