There are two kinds of stuttering. The first happens with non-Nokia applications when, e.g., locking the screen or rotating the phone. Nokia thought it would be very clever to actually freeze all applications it doesn't trust (i.e. all except those made by Nokia and explicitly whitelisted in the OS) to ensure smooth transitions. It turned out to be not so clever after all, esp. since the GStreamer sound pipe is prone to die during freezing (causing e.g. FM-Radio to sometimes not playing anything after thawing, until you pull and reinsert the headphones to force a restart of the GStreamer pipe).

The second kind of stuttering affects all applications. The pulseaudio sound system is a resource hog, and along with other resource hogs that kick in from time to time without being asked for (like hildon-thumbnailerd) it causes stuttering. Renicing pulseaudio to a low level below zero helps to relieve this a bit.

Nokia should've done their research with renicing and kernel parameters, but obviously they haven't.