I keep seeing them! Threads from years ago, that someone has posted on. And not just "any update OP?" posts. People are posting on them as if they're current, having not noticed the date.
It's easy to miss the date of course, but I wonder how people find the thread to resurrect it in the first place, given that it must be pages and pages down the screen!
If you've ever accidentally been the first poster on a zombie thread, how did you discover the thread?