Originally Posted by Dchiefransom
I treat it like entering a regular street. If the other traffic has to even let off on the gas when you pull out, then you didn't have enough room to pull out.
Exactly.
The cool thing about traffic rules, including those that apply in roundabouts, is, in the end, that they're usually the only logical way to do it. The people in the circle have to have the ROW, or the circle could theoretically jam up forever. But having the ROW doesn't mean they have the ROW to the entire circle. What would be the point of that? So if you can enter the circle without affecting anyone who is already in it, you're not violating their ROW when you enter: go for it.
But if you're not sure what that guy in the circle is doing, whether he is going to turn right out of the circle or continue within it, and, if he continues within it you would be cutting him off if he entered right now, then wait.
By the way, as much as you're annoyed by circle users who don't signal, you annoy others probably just as much when you don't signal. That's why I mentioned signalling earlier: it's very helpful.