My personal experience:
I have a 128/1024 line, so with our "good old 4k bug" and 10k upload to get the full download speed my line is somewhat at its limit. With the old amule this ended up that I had a ping to IRC servers ~3-5 seconds when amule was running and ssh was just unusable. Since UBT has been implemented the IRC ping went down to <1 second and ssh is still a little delayed but usable...