Integrated the shaker parts that I recorded last night into "I Wanna Be a Webmaster" and "TEOTW". The latter still has some sync problems on verse 1, but it's not as bad as it was. The vocal track I'd been using showed signs of having been a cut-and-paste job, and I might well have bungled it.
I think there are still some timing problems on both songs -- there's nothing like a percussion track to highlight the places where I was playing fast-and-loose with the beat. I may have to start using a click track, or something.