What amazes me is why Microsoft felt the need to change things after the pre-release was given to third party vendors.

The pre-release worked fine and the vendors had time to iron out any bugs, but you kinda wonder why their R&D bothered when the patch that got released to the public was different. Many security and business programs have started behaving oddly, become unresponsive or have simply crashed. One company reported that several customer network installations had broken after installing SP2

Included in the bug list are games such as Unreal Tournament, Photoshop Elements, Mailwasher, Norton AntiVirus and most file-sharing programs.

Current list here

One of the things that is happening with the pack is that windows is now not letting anything connect to any loopback address unless it is 127.0.0.1
This means that any assigns in the HOSTS file won't allow connections.
They all respond to pings, but the response arrives from 127.0.01 regardless of the address pinged. This is part of the problem too.

It is expected that Microsoft will release a patch soon, until such time they have recommended uninstalling SP2 from systems that are experiencing problems.