Hi. Seeing as linux application usability is in the news I thought I'd put forward a few ideas
_Automatic_ ordering by Source.
Saving state (between sessions) of "Search global" box.
Setup by default to "Download serverlist at start up" and "Autoconnect at startup" (If legally sound

Or, If not. Upon clicking connect, a dialog which says "You are now connecting, would you like amule to always connect automatically when it is run? [yes] [no] [ ] Don't ask this again"
[Same with serverlist]. On first run when there are no servers, can we have a big balloon or something, pointing to the serverlist button telling the user to click it to obtain list of servers. (If too winXPish, then ignore). I WANT MY MOM TO BE ABLE TO USE AMULE. As it is I have to write out quite a list to enable her to download stuff.
ability to enter searches even while not connected. They would sit in the search tabs and be executed as soon as a connection was made.
perhaps a larger, chunkier button which says connecting ..., while search/transfer windows/buttons help the uninitiated by:
"Searches" says "Searches will not execute until you are connected, you are now attempting to connect." or simply "Awaiting connection to execute search"
"Transfers" says "Downloads will not start until you are connected, [connection progress]", or somesuch.
If, and only if the sound device is free - play a sound "amule connection established" when connected. Similarly for disconnected. Obviously include options to disable.
Ability to sort items in incoming according to their type. E.g. Seperate folders for all the amule types Incoming/Video Incoming/Audio Incoming/Archives. Perhaps you can peek inside archives to decide if they are Video or Audio inside?
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As you can see. I have a lot of ideas. These are important for increased usability. After these few simple things, my mum will be able to use it! And that's an acheivment in itself.
Take care,
Luke.