Same thing here -- slow as molasses on my system, using 100% CPU. Athlon 1.5GHz, Java 1.5, LW 4.8.1, Sygate personal firewall (configured to be transparent to limewire). Even when reduced to "below normal" priority it seems to slow other apps down (which shouldn't be possible, unless the system is swapping, which it shouldn't be, because the commit charge is 600/1024M -- yes, I have 1GB *physical* RAM in this box).

May try going down to Java 1.4.2,

It seems to have gotten worse since browsing a host the other day and adding 4-500 files to my pending downloads list (although I didn't do anything stupid, such as set it to allow that many simultaneous connections -- they're mostly showing as "need more sources" right now, since their source seems to be only intermittently available), and worse again when I went from 4.6 to 4.8.1 a couple days ago.

The number of files pending seems to make it use more CPU, not just the number in an "active" state such as downloading, waiting for busy hosts, waiting in line, connecting, or some such. This suggests a design problem -- perhaps every single pending file is associated with a periodic polling for new sources to have been discovered, rather than when a potential new source is discovered all the pending files are iterated over to see if any are on that host, or those pending files being completely inactive except when explicitly searched for, either because a search result comes in that matches one or because you selected it and hit "find sources".

I'd rather avoid cleaning them out though, in case I don't find them again and it makes the difference between eventually getting the file and never getting the file.