I would advise on getting some traction before quitting your job. It can be arbitrary - a few thousand users or uniques/month. If the idea is good you should be

I would advise on getting some traction before quitting your job. It can be arbitrary - a few thousand users or uniques/month. If the idea is good you should be able to manage that. Although if you build something impressive enough it's worth it. Even if things don't pan out, you can use the experience to find a better job.