One question I have about the various sites is in regard to copyright? I presume all is spelled out in the terms and conditions once one signs up, but are there pitfalls and/or small print (or is that font?) to watch out for?
For copyright reasons, you should be fine with any of the major suppliers. You retain ownership of all your photos at all times.
The clauses to watch out for are the ones that read like "we can use your photo for promoting our site", if that's in there then they can use it on their front page and you'll get $0 in return. But you'll still get a lot of views out of it.
The exception is Google+, don't upload there if you ever want to sell those pics professionally. Basically, by uploading to them you give them a right to use your photos for whatever they want. Not a big deal for most people, you can still sell them and make cash.
But if you get hired by someone who wants an exclusive license to do what they
want with the files (ie, you and your camera are just tools employed by the company, the 'company' legally takes and owns the photos).
If you upload it to google+, then the 'company' that hired you and g+ both own the photos. I probably didn't explain that very well, a web search will probably find more info on it. But don't worry unless you're a real pro who can't eat dinner without selling photos.