Bit Torrent

Believe it or not, I've only really started to use Torrents for my open source downloads lately.

I learn that the torrent client should be kept open for as long as possible - I make sure that I leave my client on throughout the night to give back what I've taken.

What I was wondering though is how many of you leave your client open and for how long? Is there anybody out there who just downloads and then shuts down the client?
BTW, my choice of client is the open source Transmission. If you have any clients to recommend to your fellow otaku (or torrent sites for that matter) then please feel free to do so ^^