I'm just as surprised as you are that I didn't dedicate a paragraph or 5 or 6 to GNU Screen. I did mention it while talking about how Terminology can split like GNU Screen can, but Screen really is a champ. I've used Ratpoison quite a bit, which is the X equivalent of Screen. It's quite a nifty desktop. Super-lightweight to boot.
So have I. I use the drop-down terminal extention for GNOME3. It gets the job done for quick tasks (updating, htop/iftop) or running moc, but lack of tabs is pretty disappointing. Yakuake/Guake are pretty nice.
I've looked at tmux before. What are the advantages it has over Screen?