

Both the Nokia 5800 and 5530 just got over the air firmware updates, to v51.0.066 and v31.0.005 respectively. Both phones have full User Data Preservation, of course (as have almost all other Symbian-powered phones since the end of 2008), but the usual backups 'just in case' wouldn't go amiss. Check for the updates for your phone using *#0000# on the homescreen and then 'check for updates'. Improvements include browser and music player updates, plus the usual minor bug fixes.
More on the 5800 update
More on the 5530 update