Early adopters will experience the worst of the pain. (Adopters? There's where the whole childbirth analogy falls apart, I guess.) If you think you might want to jump right on the service pack when it becomes available, be sure to check out the list of programs that won't work after you install Vista SP1. Microsoft has intentionally disabled several common security suites (BitDefender, Trend Micro, and ZoneAlarm) due to what it describes as "compatibility problems." If you install SP1 before checking for a compatible update from one of those vendors, their problems will become your problems.
Like most major changes and updates to Windows, the best plan of action is to hold back for a month or so until the full extent of any problems becomes clear. That also gives third-party vendors a chance to get serious about fixing problems that crop up. Vista SP1 fixes more than 300 problems, including several performance issues; it's not a question of if you'll install it, but when. Windows XP SP2 was a major and disruptive change to Windows, but in retrospect it was the best thing that ever happened to XP. In the meantime, I will prepare for XP SP3 and get an epidural.