Close button sends client to the tray, statically linked Qt for OSX.
See the Changelog for list of features and fixes currently only available in the nightly builds.
One other way to remove uploads is to check the 'Clear Complete/Aborted Uploads' box and wait about thirty seconds, which I don't feel is ideal either. I do want to add a clear complete/aborted uploads button that does the same thing right away, but I have my doubts regarding the usefulness of letting the user remove specific uploads.
As for moving users up the queue, you can put a user in a group with a higher download priority. See this announcement for details.
I was more so referring to incomplete uploads. It's just a bit annoying when a users may have 30 tracks queued up and a fellow friend is waiting to download only 1 or 2. Going to read up on the user groups now :)
tommynumber, this should be solved either by groups or by a built-in algorithm allowing one-track people to download faster. Nobody looks at the upload screen for hours I believe, so why to improve something in that unpopular place? IMHO.