This post from Steve Blank is a good summary about the growth of a startup to a more established company and how it doesn’t just happen over night. It looks like this will be a series of posts, so keep an eye on his blog or this space for the follow-up posts.
I think one of the points that is alluded to, but perhaps not stressed, is that during this process, many times the original founders will get politely (or less politely) dumped out of the organization, as the personalities that can get a startup off the ground can usually just as quickly create a large crater when they drive it even faster back into the ground. This perhaps hurts some feelings, but makes sense in terms of what will allow the business to grow.