Flat tire
Wow I just checked out my flat tire. There was a huge glob of Stan's goo mixed with dirt stuck to the outside. Turns out it actually sealed up, but there wasn't enough air pressure to ride any more.
I peeled the goo away and found a gash about a centimeter long. I'm impressed it sealed up at all. I'll boot the tire and it'll ride again.
This is my second flat in three years with the notubes system. The first time, I got a hole in the sidewall while in Forest Park. Second time, well that was today. I never have to worry about riding over thorns or stuff like that, because it gets sealed up immediately. That's pretty nice.

Also, you can put duct tape or something inside, and fill the hole from the outside with superglue.
I built my own wheels, and haven't had any true issues. Considering the abuse they've had, I'm pleasantly surprised.
So you're ditching the setup? I'd reconsider. Or, I'd sell me your used rim!