Personal experience: I had to replace the h/s on my 'cross bike awhile back (contamination lead to corrosion). There are a number of different integrated headset standards out there ... if you don't know what you have it can be a hassle trying to pick a replacement. Then there's the issue of options. In my case, there were very few. I either had POS TH Industries or Ritchey Pro. Luckily, I like the Ritchey stuff.

Edit: I'm sure Keith has some good input on the topic. I'll ask John + Phil tomorrow and see what they've come across over the years.