I've been a programmer professionally for over 10 years and worked with a variety of teams. In my experience, I haven't observed a correlation between tinkering with programming as a hobby and the ability to be an effective employee. From what I've seen, communication skills, interpersonal skills, and the ability to motivate oneself have more impact than hobby programming.
"I wouldn't take my car to a mechanic who takes his own car to the dealer." -- I see your point, but use your imagination a bit more. Perhaps there are really good mechanics out there who really love being mechanics but at the end of the day want to do something different than work on cars. In other words, you can love something and be good at it without it consuming all of your waking life.
You have to be careful with taking such a hard line. As a developer, I would hesitate to work with you.
EDIT: For the record, I work on lots of side projects outside of work.
"I wouldn't take my car to a mechanic who takes his own car to the dealer." -- I see your point, but use your imagination a bit more. Perhaps there are really good mechanics out there who really love being mechanics but at the end of the day want to do something different than work on cars. In other words, you can love something and be good at it without it consuming all of your waking life.
You have to be careful with taking such a hard line. As a developer, I would hesitate to work with you.
EDIT: For the record, I work on lots of side projects outside of work.