Forums like this and user-submitted reviews on shopping sites are often echo chambers that unduly amplify problems. The vast majority of users don't go online and post their positive experiences. The users that are having problems are the ones posting about it. Me, for instance. I got my SP4 yesterday and have had absolutely no problems with it. This is the first I've mentioned it anywhere and I probably won't be posting about it until I come across something I need help with.
My first job out of college was working phone tech support for a major PC manufacturer. At the time (1994) we were shipping 5,000 PCs a day. We heard from very few of our happy customers. I had some co-workers who developed the jaded opinion that our products were crap. After all, look at all the people that were calling in. When was the last time someone called tech support just to say their computer was working perfectly, thank you very much?
I know the squeaky wheel gets the grease, but I'm not seeing major trends that would indicate systematic, wide-spread problems. If there were some show-stopper bugs in the SP4, we would see LOTS more people going online and flooding forums like this.
Sometimes it hurts to be on the bleeding edge. A month or two from now, I'm sure the bugs the early adopters are seeing will be fixed. You might want to hold off a few months and get an SP4 once the kinks have been ironed out.