For those of you who actually care about this stuff (as I do), here is the list of fixes that SP4 takes care of.
http://support.microsoft.com/?kbid=327194
I have installed SP4 on three test machines and four production machines. All of them have Norton AV corp v8 and Novell Client32. I thought for sure that it would choke on these boxes but the install went without a hitch on all seven machines. I'm beginning to get that wonderful false sense of security...