i don't know if this has been suggested but how about having a favorite forum section on your homepage where you can put all your favorite forums so you don't have to spend all this time searching for them.
This idea seems like it will hold water around here on AG. I'am not sure though if it has been suggested before Monocycles, but it's probably not a major issue on AG.
You should contact Carlie or Daniel and personally ask them if they feel it will hold water or burst through.
If you type (or copy and paste) that link in, it will show a list of forums and threads on AG that you've been to recently. The neat thing is, the ones you've been to the most are at the top! Technically, the feature was already there, it was just hidden for you to figure it out! =)
The idea of bookmarks is built so that sites don't have to implement these features to make users happy. It saves space and coding. I suggest you do it, because there is a guarantee that there will be no bugs or errors.