It would be a good idea if friends who are already playing had a red spot next to their names so you would know who you could invite - save all this waiting for a refusal!
That is listed on the road map section of the upcoming releases.
Along those same lines...doesn't the "available to" icon control who is available to be invited and who isn't? I switch mine to "no one" when I'm playing in a ranked round so as not to make my listed friends think I'm ignoring them. Or does it not work that way?
You are correct. The downfall of this is that your friends do not know you are online. When they have a different color dot for 'in game' it makes it easier to know who is online and when you can invite them for a game.
Cool, I was hoping it did. Not that any on my friends list are actual "friends", but I don't like to ignore people if they are trying to contact me. Jonahvark's idea of colored dots would be helpful, though...good thought.
This idea was first proposed by Nivlac in December 2008, and later expounded upon in another thread in July 2009.