A few ideas...
 

Hmm... how with a button under the download screen to put a recently downloaded file in the playlist? its much easier to search the new files in a 10-files-containing-list than in a list with over 2000 entries....

and my second idea is to introduce some kind of cache into the gnutella protocol (although you cant do this, but just bringing this idea to someone who can change this :P)
it could be, like the program connects to someone else and saves his filelist, then disconnects again.
if now a query reaches the servant keeping the saved list, it wouldn just look if it maches with his own list but compares with his own and the saved list.
to proof if the other servant is still online, it could send a special kind of ping that doesnt go broadcast but contains some special info to figure out if the other machine is still the same.
this would help to setup a network double the "size" it has at the moment but keeping the bandwith down.
maybe a stupid idea or something that couldnt be realized....
Nils

Hm yeah this button would be great.
and a search-resume thingie... like IRC/bash does it: if you press the cursor up in your search form, it shows the last performed searches.

and LimeWire doesnt remove connections when you mark one and press delete, it would be a great improvement.