Like my status updates...only better!
Part of me feels that not calling back is ruder but ultimately kinder. As much as I hate it in the moment, I also don't like being strung along. But dude, if you're going to call, don't say you forgot about the person. Say you got busy, say you've been thinking about them. Do not use the term "forgot."
I'm with Lollipop on this one. If I never get a call back, I figure I just wasn't his type or he just didn't care enough TO call back. Yeah, it's rude...but it's better than being told "yeah, sorry, you were completely forgettable and I forgot".