I wanted to provide a link I found today for a KB article that lists the fixes included in the .NET Framework 1.1 SP1 package, you can find it at http://support.microsoft.com/?kbid=867460. This article has a pretty good list of individual issues that have been fixed in SP1. It does not appear to be 100% comprehensive however.
For example, I know that the issue described at http://support.microsoft.com/default.aspx?scid=kb;en-us;827072 has been fixed in 1.1 SP1 (the ASPNET user account no longer causes the XP welcome screen to appear after installing .NET Framework 1.1 SP1 if there is only a single user account on the machine). This particular issue has been mentioned a couple of times in the newsgroups, and it was actually a bug that the account was not installed with the bit set to mark it as a hidden/system account. This account is used to run ASP.NET worker processes on the machine that serves up ASP.NET pages.
Anyway, I hope this helps….