Company 1: Started by myself, partnered with a sales guy 50/50 after a few months. Company took off after the sales guy because he was able to close large contracts.
Company 2: Started with two other people I knew well (doctors) who were in the field but non-technical. I ended up leaving company after 3 years. This was in part because they couldn't put in the same amount of work (never partner unless they can contribute full time).
Company 3: Started by myself, raised money by myself.
Moral of the story: Partner with a sales guy if you have something to sell, and make sure they have a proven sales track record. If you're building a product that won't be ready for a long time, work on it alone and test the markets as soon as you can, then partner. There is no right answer, but don't partner with somebody simply because they are on the business side. It's also much easier to pitch with a sales guy. And don't partner simply because the business guy has an idea.