WSUS SP1 Readme is updated (on 21st June 2006) with known issues once you apply WSUS SP1.
Readme for WSUS Service Pack 1: This document describes known issues affecting Windows Server Update Services Service Pack 1 (WSUS SP1).
New Known Issues:
Issue 6: If you are using a proxy server, the SP1 upgrade may clear the proxy configuration username and password
Issue 7: How to recover from a failed upgrade to restore your WSUS server to a consistent state and then retry the upgrade.
Issue 8: WSUS SP1 upgrade can fail in some cases when the WMSDE database has been migrated
Issue 9: WSUS SP1 is not updating WSUS servers which are setup using remote SQL deployments
Issue 10: Changing the computer name prior to upgrading to WSUS SP1 can cause the upgrade to fail