I'd be surprised if this didn't happen to everyone at somepoint. What usually happens to me is that I always have 2 or 3 projects going. 1 I am working on constantly and 2 that I don't work on at all. Sometimes I just forget about other projects until I find them sitting on my disk looking pathetic and half done.

What I have done of late is force the issue. I primaraly use perl for CGI, so I tell my users (vaugly) what I'm working on and tell them when I should have it done. If I don't get the project done on time they get all bitchy and that keeps me motivated.