from what we've seen and what we've heard, basically starting at $1 million/year in revenues, you will hit a serious new set of problems (some call these inflection points) at every doubling thereafter (i.e., 2M, 4M, 8M, 16M)
obviously there are exceptions (some businesses are simply born to be able to handle massive amounts of revenue in a flat manner) but basically, every time a business doubles, the problems change. this doesn't mean you're incompetent, or that you lack skills.