If you run an application that actually sucks CPU (and most don't, except when you're interacting with it), then there could be slowdowns obviously (maybe your Youamp is a CPU hog?) The other way of getting a slowdown is if you overflow RAM and start using swap space.

The kind of applications I have running (Skype, Maemo Mapper, browser, email, plus the dozens of daemons) aren't slowing down my N800.