E&O is expensive, but useful. Our company has it - we wrote for Microsoft's bCentral sites for 2 years a while back and it was a requirement of our contract. We decided to keep it and we are glad we did.
One thing you may find is that in attempting to get contents or generally liability insurance, you may be required to get E&O. This can get very expensive, but we found that by shopping around (and not listing to the BS of our original agent) we found rates that were significantly lower than what our initial agent was charging.
I actually run a small business and I decided to get an errors&omissions for my business insurance after one of our ex-lawyers got us in big troubles that led to an even bigger money problem that would have been easily dealt with if only I had an E&O insurance.
You should consider it if your business works a lot with other profession men, such as lawyers, engineers etc.