After re-reading some recent questions in On Startups: Startups and full time jobs and Starting with no real industry experience I came to the conclusion that full-life employment are incompatible with part-time startups. If you feel drained at the end of each an everyday after work, there is no energy left for entrepreneur activities, actually for any activity. This is usually the result of the "Software as a Sausage" approach of management.
My two cent on the matter, from my answer to starting with no experience:
If your regular, full-time job is so demanding that you cannot be quiet in the weekend without having to answer email from the company, endless times you have to stay more than 10 hours at the office, not only it is an unhealthy job but also is a job that won't allow you to create your own company some day.
Were you to start a company little by little, you would need to have a more compartmentalized work, regular hours, no bouncing schedule. Otherwise, you will end with no time for a startup, not even a decent life.
Note: The links to OnStartups are broken since the site is no longer maintained.