bitcoin-Qt is using all my upload bw WHY?
Probably your relaying transactions. My upload bandwidth was peaking around 1.7Mb. I had over 60 connections so I limited my connections to 20 and the transactions I relayed went down from over 15 a day to 1 to 6 every few days.
So what is your connection count? Do you have TCP Port 8333 open and forwarded to your IP that the client is on?
If you don't like the upload traffic then you can stop the port forwarding.
Sam