I mentioned wanting a BT client with a little more bang to it. On BTFaq.com, I found mention of a client called Azureus. It's in Java, and has Linux, OSX and Windows packages (as well as source packages). I set that up, and was just floored.
Azureus shows you lots of info about what's going on. Perhaps too much for some folks, although you can just leave up the summary window, and be happy. But it's very configurable. Limiting upload and download bandwidth (which I need to keep Wife happy when she surfs); limiting the number of currently active downloaded torrents (and torrents you're seeding); queueing up torrent to both download and seed (more on seed queues in a moment); how often to update the GUI; and lots, lots more.
The BitTorrent world likes for you to leave your client open when you finish downloading, so that you can upload to others and share what you just got. As others have said, that's why it's called file "sharing" instead of just file "downloading" or somesuch. But it's possible to download lots of files, and then the question arises of which ones to seed.
Azureus is cool in that it lets you keep your torrents "active", and seed just a select few of them. The default is to seed the torrents with the lowest seed:peer ratio; a torrent with 1 seed and 10 peers needs your assistance more than one with 10 seeds and 1 peer. And it'll let you boost the priority of a torrent that you're the only seed for; (go ahead, be a hero!).
Anyway, my brain just loves sitting there watching Azureus run. I love tweaking the settings, adjusting which torrents are seeding, figureing out what to fetch next, etc. In truth, I've been having more fun running Azureus than in watching/using what I've been fetching. (What have I been fetching? More on that shortly.)