[@Dervish] You know, I haven't looked at it from that perspective, mainly because I have very limited experience with Free/Speed post RP's. The closest I've been has been RP in MMO's, which did indeed take up a lot of my nights as a teenager and helped me improve as RP'er, though not necessarily as writer. As for the few Free RP's I've participated in, I guess I was blessed by having some very competent writers involved; what struck me was how concise these people were. As you said, there's not a lot of room for description, so you have to make the most out of those 2-3 sentences to get your point across. Honestly, I find that immensely hard and it's easier (and faster) for me to write out a few paragraphs rather than trying to cram it into a couple of sentences. 

But again, this just bring me to the point that it's all very subjective. Trying to pigeon-hole a creative process such as writing seems like a pointless exercise, that's why I'd say the OOC aspect of it is a lot more important, which seems to be the prevalent opinion in this thread.