Yesterday I was messing around with a new frontend for a database, and ended up trying to float approximately 7000 elements. Apparently that's just a bit too much for IE8, since it ended up using 1.4GB memory when the page was fully rendered. Once I removed the float statements in the stylesheet everything was back to normal - IE8 using about 16Mb memory.
I didn't even try whether this had the same effect on other browsers - could be a fun experiment one day though, to see just how much they're actually capable of rendering without wrecking the client pc.
Anyways... note to self: Don't float too much!