WordPress 2.8.5 was release on the 20th October 2009. After considering for a few days I finally upgraded, I upgraded my development site first and proceed to check all plugins and making sure that they are all running smoothly first before I upgrade my main site.
This is actually a security release, hardening of WordPress. For official information and details you can click here to go to wordpress official site to read up more on this release.
This release fixes the following as mentioned from the official site.
A fix for the Trackback Denial-of-Service attack that is currently being seen
Removal of areas within the code where php code in variables was evaluated
Switched the file upload functionality to be whitelisted for all users including Admins
Retiring of the two importers of Tag data from old plugins
If you are considering upgrading also, Please do make sure that you backup your database first before you upgrade. Safety first.