The Nokia 5800 just got a firmware update via both Nokia Software Update (100MB or so) and over the air (6MB), to v31.0.008, for many worldwide product codes today. Changes are listed below, but do please comment if you notice something extra that's new or shiny! The usual caveats over backups apply, though the 5800 has User Data Preservation, so don't worry too much about your data.
To update over the air, type *#0000# from the dialler and 'Check for updates'. Good luck!