Yes, I have found 500px OK but not that rewarding in the area of constructive comments - maybe it changes if you pay for the Premium membership, but I can't see too many benefits to it. My main photo discussion place remains RedBubble (
http://www.redbubble.com/people/analog6), I get quite a bit of feedback - it is a good community once you build up your watchlist and contacts, and I do sell occasionally (2 cards this week) and it allows me to make great calendars. And it remains free - a big plus for me.
Bob, I liked your shots of Hilda's ceremony, very nice work.