Nokia released a new firmware V52.0.007 for Nokia 5800 XpressMusic. The firmware is available to download via OTA. You can also update this firmware by going into the Applications --> SW update. It is shown there as "Phone software".
The size of firmware is 4873 kB. Since firmwares are very important to your phone you should always update to new firmware available. This firmware will improve phone's performance and bring new features such as better touch screen experience, Enhanced rotation, etc. Though the official changelog is not available but there are number of small UI changes that you will notice after updating to this version.
There is another update available via SW update. It is "Music Player Update v15.2 (1034)". The update size is 687 KB. Always wanted to know the lyrics of that special song? This new feature displays the embedded lyrics of the song playing on your device. Download the update and then click on Options menu of Now Playing view to enable this feature when lyrics are available.