Anita Campbell's Selling to Small Business Blog has a post on size definitions for small business. While this is a rather arcane topic, it is actually is quite important. Many times I've seen people get very confused because they use differing definitions of small business.
We define small business as less than 500 employees. We do this mostly to be consistent with governement statistics. We define mid-sized as between 500 and 10,000 employees. We use personal businesses to mean single person companies, or what the governement calls "businesses without employees". We chose not to use the government's name because it is too long and too confusing.
We use micro-businesses to refer to businesses with 5 or fewer employees. Our usage includes personal businesses in the micro-business category.
On a pretty much unrelated topic, I was recently on Anita's Small Business Radio show. It was great fun and my 86 year old mom listened in live. She was told me I was "just like Jack Benny except he was funny". Not sure what this means, but I am taking it as a compliment.