It, being a Microsoft enterprise hotfix rollup for Windows 7 SP1 and Windows Server 2008 R2 SP1.

And the 15% logon time improvement was just when I applied it to the Windows 7 client.  We’re yet to apply it to our Windows 2008 server farm.

I first saw this hotfix mentioned at the Microsoft “Dude where’s my PFE?” blog.

Update 18th April:
It may cause issues with esri’s suite of products (ArcGIS, ArcInfo …)