It's the RAM, baby!

Ever since Wrath of the Lich King came out, my game experience has suffered from (sometimes very) very low framerates, alt-tabbing to Firefox taking up to 5 minutes, and the known phenomenon that flying in or out of Dalaran just hangs the game a lot. As in, unplayable at lot. Well, I just put in 4 GB of RAM into the machine instead of 2 GB, and lo and behold - all of this is gone. I fly up to Dalaran, land, mount my charger, and ride off, without an hickups. And then I alt-tab to Firefox, check a quest on Wowhead, and am back in the game seconds later. I really hadn't thought it was only the RAM, but it seems it was. And yes, this is on Vista 64, before you ask. That OS can indeed use 4 GB.