I find that it's hindered my ability to write other things, almost completely. Though at the same time, it's helped in a lot of ways as well. Ever since I started RP'ing, I have made/had less time for regular old writing, because when I am online and writing stuff, it's usually related to RP.
But when I do sit down and write, I've found that my characters are so much more interesting now than they ever used to be, and I have an easier time getting into them. They are definitely more three dimensional than the characters of my pre-RP'ing days, much more realistic and much more flawed. So I guess RP'ing has helped me to develop more true-to-life characters...when I can be bothered to write about them!