jake14mw: A 200a residential service usually means 200a at 240v, so when adding up breaker amps, divide the amp rating of 120v breakers by 2. So, for example, a 15a 120v breaker should be added up as though it were 7.5a. As wwhitney wrote, the NEC is somewhat complex in evaluating a more precise load calculation in trying to determine when one's service is inadequate for adding additional loads (like EVSEs).
I guess it goes without saying if your main breaker starts tripping, your service is probably overloaded! The question is how to avoid getting into that situation...
Without getting into complexities that the NEC does:
A 200a service is roughly 240v x 200a = 48,000W. If you add up all the power of all your lights, appliances, EVSEs, etc and the sum < 48,000W then I think you may be OK (unless I need some simplifying factor that wwhitney may be so kind to mention). This assumes everything is on at the same time. If you are over this figure (especially by a lot), then you need to do more thinking/more calculations concerning the possibility for overloading your service...