It is released on 2009-05-27.
There are some bug fix. I just upgraded my OpenX installation afternoon. It is very simple to upgrade from v2.8.0 to 2.8.1.
# Bug Fixes
* Zone probabilities are distributed amongst campaigns, independent of the number of banners. OX-3095
* Fixed delivery of exclusive campaigns when banners have delivery limitations. OX-5450
* Inventory lists now react to last visited parent. OX-4788
* Displaying entity IDs in the UI is now optional. OX-5341
* Fixed function declarations for various _adRenderX functions. OX-5355
* For more information, please see https://developer.openx.org/jira/browse/OX/fixforversion/10843
# OpenX Market Integration
* Market campaign management tools, which allow you to set floors for multiple campaigns at the same time.
* Ad quality tools, which allow you to review ads that have run on your sites and block advertiser campaigns.
* Ability to re-associate your OpenX.org account to OpenX Market even if you had to switch instances of your OpenX Ad Server (i.e., due to a reinstall or server change).
* For more information, please see http://www.openx.org/market.
# Major security fix. Removed vulnerability that allowed anyone to log in as an admin user. See https://developer.openx.org/jira/browse/OX-5460