I believe they look more at ability mechanics than actual champion ideas.
Im sure everyone on staff has a million ideas each. But you cant even include
everyone's ideas on staff.

Brackhar recently posted on a few champion concept threads. Pretty sure he helped design a few champions? So yes, they do read them.. just rarely respond, I guess. They already have 9+ characters on the design table.. so they aren't exactly hurting for ideas yet, though some concepts are pretty cool and might spark some interest =)

Dota had a ton of suggested champions that made it into the game. Riot has done a tremendous job in looking at the suggestions from their beta testers. Even if they don't take certain champions and make them in the game, I'm sure our ideas at least are getting them thinking about what to make. And more importantly what their community would like to see in their game. If nothing else, thinking and creating champions is a fun idea to entertain.

I think Guinsoo and some other designers read every single suggestion and take note of the good ones.

We are not quite ready to put user-themed ones into the game, but we will be in the future and we will go back through all these awesome ideas =)

so is this really the place for them or should they be in the open suggestions forum or whatever?