It's a feature that I've seen around that I wish PT had greatly. The recent posts on the right help, but when I've been gone for a while it's nice to see EVERYTHING I've missed. I've never actually seen the PHP code for it myself, but I'd imagine it couldn't be too complicated.
Perhaps also being able to see a list of the recent topics you've posted in would help (say over 2 days or 5 days etc).
We should be able to get that and other nice tings in the new forum. But I can't say when that will be...
But there is another way to find out what you have missed. Go to the forum home page and look at threads and the dates listed next to them.