That friggin drives me insane. I've posted several things where I'm asking a specific question (and stating that X, Y, or Z won't work) and the first thing that get's posted is "You should try X?"
Happens in PMs too.
My absolute favorite is when someone posts a question about something (and there's 3 other posts with nearly the exact same question in the title - right on the first page of that section).
I think more than anything it's people trying to get their post counts up so they can have a sense of accomplishment and to use the classifieds.