How do you manage your bankroll?

[el_grande]

OK, I'm familiar with the 300BB bankroll idea. I use it. Well, maybe I use more like 200BB, but I play on party. :-)
Mathematically, 300BB is supposed to keep you afloat as long as you are playing fairly well.

Let's say you move up a level. I just did this. I started with $100 at party playing $.5/$1 and ran it up to $500, where I switched to $1/$2. Now I just started playing $2/$4 and my BR is 300BB for that.

I would not have started playing $2/$4 with 150BB, so what happens if I go on a horrible streak and drop to 150BB? I'd be in a situation where I'm playing a game too rich for my BR. So if you were in this situation, would you drop down a level? How low do you have to get to do this?

Is there a modification to the simple 300BB rule where you regress to previous levels when you hit a certain BR? Should there be?