In theory their voting system is the fairest I have seen for comparing and ranking images. In reality is doesn't work well. You have to have spent money with them or have a facebook account you are prepared to link with them to be able to vote and still much of the voting seems random or even perverse. I have seen several images with obviously fake and badly positioned water reflections become part of their all time top 1% - so ridiculous I suspect the system is being gamed.
Compared to other photo sites it doesn't have a lot of users and seems to be in decline. My overall verdict - don't bother.