I discovered this when I was having problems with my install of Winamp where it would crash whenever I attempted to advance a track. To remedy this I decided a reinstall was in order and re-downloaded Winamp. I started to get suspicious when I noticed that the Winamp install executable was labelled winamp531_full*_emusic_7plus.exe (The word denoted by the asterisk will differ depending on the package you choose which can be either "bundle", "full" or "lite"). After performing the installation I went straight to the "About" page and, sure enough, the version number was 5.31.
This new version, unlike other releases, was not reported on the front page. The front page still says "Nullsoft Winamp 5.3" which is the same for every other part of the site minus the version history page. Yet still when you download Winamp you will get version 5.31. This is surprising as it is not a minor release. Version 5.31 has 25 bug fixes and now has the ability to encode and decode FLAC files (So therefore it has support for FLAC files yet the list of supported file types on the download page does not reflect this). The new version can also read and write to the disc number property of ID3 tags (The technical description from the sixth line of the change log is: Improved: [in_mp3] support for reading ID3v2.4 per-frame unsynchronization). iTunes has been able to do this for quite some time and it is a feature I have been looking forward to in Winamp.
I am unsure of Nullsoft's reasons for not making their usual hullabaloo over this release, or even if they had any reasons at all. Maybe Nullsoft is just being lazy. My crackpot theory is that AOL, being a commercial company and owning Nullsoft, is profit driven they are scared by FLAC because it is free both in a money and DRM sense so therefore they want to keep this update quite. I've always been suspicious of Nullsoft ever since they were bought out by AOL. Then again I've always been crazy. Never the less if you are a Winamp user you should still download the latest version from winamp.com. Despite what the site says you will get version 5.31. I have checked the downloads for the Bundle, Full and Lite packages of Winamp and they are all version 5.31 (I didn't check the Pro package because it costs money). You can see the changes that come with version 5.31 at the version history page."