When I use apps like Deluge, Transmission or KTorrent, the wifi stop working! Someone know why? (sorry for my english, in not a native)
A lot of wifi connections and their routers fall over if you throw too many connections at them and a lot of bittorrent clients are set to unlimited connections by default. As soon as you start something up, it'll try to connect to 600 peers and everything implodes.
Fairly simple fix: limit the number of connections. I'd suggest a global max of 100 and ~60 half-open connections. I have had bad routers that only support half that so you might need to rein it in even more. In my experience this doesn't usually hurt your speed.
You might also want to limit the upload bandwidth. I've got 1mbps (128KB/s) upload but anything over 50KB/s slows things down. I limit my upload to 20KB/s and everything keeps on going.