I'd like to add to the 'beta as cheerleaders' thing that it's not so much encouragement I necessarily need as someone to brainstorm with.
"Okay, so you think pairing this guy up with himself would be hot, and I agree and would like to write it, but how're we going to work that into the plot?"
"Well, there's that cloning facility they used that one time."
"Good point! But an alternate universe version of this guy would be fun too, what would they be like?"

And so on, I need people to brainstorm with/encourage me as much as I need a beta reader who can tell me when my canon or my characterisation or spelling/grammar/punctuation is off.