I'm in the process of paring down a character's too lengthy description, and it's gotten me thinking about descriptions as tools for good roleplay.
I know I personally tend to check descriptions out before I get down to RPing with someone, and I really love being able to work details from them into roleplay. I try to keep in mind that characters aren't, from their own perspectives, wisps of coding - they're physical beings in a physical universe, and their first reactions to other people will normally be based on things like height, or build, or clothing, or whatever. (For example: I have a character who's tall for her race, and grew up in a relatively homogeneous area; she thus subconsciously finds it unfamiliar - and rather uncomfortable - to have to crane her neck to look someone in the face. It's fun for me when a character description mentions a height - whether exact numbers or just "So-and-so is tall for a ___" - because it gives me some idea of what her reactions should be.)
I'm not very interested in seeing psychological examinations or histories - what can I do with that material that isn't OOC? - but I jump for joy when I see a description that mentions what kind of voice a character has, or what their posture is usually like. Details don't have to be special and exotic to give material for roleplay, either; glowing eyes aren't as interesting to me as a character who smells a particular way.
How much do you make use out of descriptions when you're playing? What sorts of things do you hope to see when you click that eye icon?