The computer gets a bit slower when there are tens of limited connections, and pingtimes suffer too. I guess it works at driver level, so that probably involves processing every fucking packet going through the stack... not that it makes anything unusable, just a bit less responsive.
Plus, I have bandwidth control on every silly P2P program on the planet, which basically means doubling the effort for nothing.
I just discovered that the latest DC++ (0.6811) has some sort of upload limit, but it's implemented in a silly way with predefined values. Better than nothing, I guess.