I took the plunge this morning and made the upgrade from XP SP1 to XP SP2 RC1.  I'm using Roadrunner high-speed cable, so the download and install process took about an hour, and everything went well. 

If you elect to save the files(just in case there's a need to revert back to XP SP1), a $NtServicePackUninstall$ folder is added to C:\WINDOWS.  In my case, the folder is 397 MB.

If you've personalized the cookie settings in Tools - Internet Options - Privacy, you'll need to reset them.

Some new settings have been added to Tools - Internet Options - Security, so you'll need to check them.

Internet Explorer and Outlook Express have been upgraded to version 6.00.2900.2096 and Media Player has been upgraded to version 9.00.00.3133.

Several new listings were added to SERVICES.

The Windows update site has upgraded to version 5.

MSN Messenger 6.1.0211 refused to load, but I fixed that problem by reinstalling it.  All my other programs seem to be working okay.

Frank's Windows 95/98 Tips (Also a Windows XP user)