Completely agree. The other problem I've seen with getting stuck on the same project for X years is that you'll have a very limited portfolio to show for it, unless you're working on side projects as well.
If you are on a project for a few years (and aren't doing just maintenance, in which case I'd GTFO) you should be able to show a roadmap of where you took the project, its success etc. which might not be so bad.