Okay - so here's what I think it means to be an estabished hosting company:
Been in business for a few years (at least 3 years - more is better);
Have at least a few THOUSAND customers;
General review sites and testimonials are good;
Won a few awards over the years (look for PC Magazine, CNET, TopHosts top 25, etc.)
Great Better Business Bureau scores and reputation;
Appear in the general advertising at major publications (Wired, PC Magazine, PingZine) and online at the major hosting directories (
www.tophosts.com,
www.webhostdir.com,
www.thewhir.com and
www.cheaphostingdirectory.com)