I brought StartSSL to my last 2 employers for internal sites, like development sites and internal apps, and it's been wonderful. We haven't found any problems with StartSSL certificates in browsers, from IE6 up through the newest browsers. We've considered using StartSSL for our public sites too, but haven't done so yet.

Do customers really care about the name brand or "warranty" of the SSL certificate? What percentage of customers are even aware of who issued your certificate, and do those customers really have concerns about StartCom?

This sounds like the argument we heard from DynDNS salespeople last year, about how our customers expect us to be using "enterprise" vendors, rather than "consumer-grade" vendors like Amazon Web Services. Even our savviest customers have never asked us who our DNS provider was.