My Nokia 5800 is now 10 months old and I have started feeling that the navigations are too slow. So just wanted to try with the master reset, so took a back up of the phone first thinking it would wash out everything. But not to worry as it has not removed anything from the phone and now the navigations are good. Do you want to try that too?
Go to Settings -> Phone -> Phone Management -> and select Factory settings. When you click Factory settings this will say “Restore all original phone settings? Phone will restart.” Click yes which will reset all your settings and restart the phone.
The only change I have noted is that all the profiles are set to default, none of the images, videos are lost and even the music player playlist exists and the phone seems to be new. Try this out to feel your phone brand new.