I suspect part of the stuttering is because disk IO on the eMMC causes the media player to run out of data when playing music, if other tasks are also doing disk intensive jobs. On flash memory a lot of small writes like the web browser cache clogs up the system easier than a larger, faster, single file read/write operation does, so both the app manager and web browser are notorious (in my testing) for causing stuttering as they do exactly those sort of operations. Also the very tasks which do a lot of small writes are also likely to use a lot of RAM so potentially also trigger SWAP memory usage, which means yet more writing to the eMMC, I really wish Nokia had kept the SWAP partition on its own flash chip but I guess that would have been really expensive.

So what can we do about it? Try moving your music to a microSD card as that would eliminate eMMC lag as a potential problem as far as possible. I haven't tested myself if it helps as it only seems to lag badly when using app manager, the web browser its just the odd glitch here and there, I can put up with that.

If that doesn't help I have had similar problems on desktop Linux too which clearly were not disk IO related, so it could still be that the something is stealing too much CPU from the sound system when it should be really higher in priority than most everything else to keep sound ticking over smoothly. Hopefully the PR1.2 firmware will have more optimisations to minimise the problem.