Who else uses the "was X a good sport" feature?

I use it all the time if I have been beaten by a better player.

I also use it for that purpose but try to limit myself to one a day (to report for things like abandoning or stalling).

When we do the thumbs down on the sport question, it then offers a "block" option - if we avail ourselves of that, does it block that user from being matched with us for future games or is it just blocking the chat function?

May be obvious for others but - like I said - I'm kinda new here.

it will block you from matching with them in online play and chatting, however, they can still talk in other forums that are not yours, so you may see them in forums. and it doesn't block you from pairing with them in tournaments as tournaments have specific pairings and not playing a blocked player would mess it up.

I use it mostly to “thumbs up” because a lot of people report and complain about things that they should not (like not resigning). I haven't had any problems during games so I never report anyone. But once in a while I might “thumbs down” someone if they immediately abort a game.