I have always had long relationships relative to people my age and haven't had all that many, so I can't say I have a whole lot of "data" to go by. Also, except for two times I was the one doing the dumping.
It REALLY depends on the circumstances. If you're the one that called it off, it will be easier to get over it than if you're the one that got dumped. Also, why did it get broken off? I dated a girl for about 9 months my sophomore year of high school, broke up with her, and was open to dating someone else pretty soon afterwards....but that's part of why I broke up with her: I was interested in someone else (*waves to onodrim*
). Before that though, I was in an 8 month relationship the summer after 8th grade and into freshman year of high school. She's the one that broke up with me and I would say I wasn't really over her for quite some time afterwards...at least until the summer before my sophomore year, which is incidentally when I started to be interested in that other girl I mentioned. Now, though, I think I could probably get over an 8 month relationship much more easily if I were in that position. I am certainly more mature and having been in a relationship for 6 years now, 8 months seems like nothing.