Spot on, I commented on some of the problems I'm facing on quora....e.g. "You also have your day job keeping an eye on your proceedings, and if its a good place to work you will inevitably get sucked into putting some extra effort in towards the end of projects, detracting from your startup."
I have two great clients at the moment who I am doing contract web development work for and since they're also both startups it works quite well and I can contribute a lot in terms of startup experience as well as just development, and I think that is valued. I'm always aiming to do my best for them and help them move forward as fast as possible, but there is definitely a clear distinction between that work and my startup.