It's been a huge mystery for the past 6 months. I figured it was either TextDrive or something else I'd done to make blogging to FactoryCity so painfully slow (something invisible to everyone but me). But, after stumbling upon a great list of plugins (via Digg) I discovered a plugin called NoPingWait that solves the problem by delaying the ping action until after the post has essentially cleared the runway. MarsEdit is also running a good clip once again.