As you can tell, there are a lot of ways to smoke a brisket, and a lot of it depends on the quirks of your smoker. The key in just about all the replies above is only use IT as a guideline. Probing for tenderness will tell you when it is done, paying particular attention to the flat. The point will probe tender WAY earlier than the flat, sometimes by as much as 20F IT. That's due to the higher fat content of the point. Don't worry about it. The point can take all kinds of heat abuse and still come out tender and juicy due to the fat.
The most common error folks make when smoking a brisket is using IT as an indicator for doneness. Then they slice it, taste it, and say they cooked it too long because it was flavorful, but dry. Nope, undercooked. An overcooked flat will taste dry, but will crumble when you try to slice it. It will be extremely tender because ALL the structure melted out of it.
Probe the point first, then the flat. You'll quickly understand what is meant by "it is done when the probe slides into the meat like it would into warm butter." When the flat does that, bingo.
