Gotta agree about the Nit-Ize tailswitch. It's nothing to write home about. Mine hasn't failed, but probably only because I don't use it!! I've replaced it with a TerraLUX switch that's built like a tank by comparison; I use that switch on several of my MiniMags, in fact.
The Nite-Ize LED lamp replacement ain't so hot either, really. Like their C- and D-cell replacement lamps, it runs forever, but it's not very bright. Compare one to the new MiniMag AA LED, there's no contest: the factory MiniMag blows the doors off the Nite-Ize. Of course, it also costs $25 or so... but you sure get a whole lotta light for the money!
Whatever you do, avoid the Nite-Ize "IQ Switch". It's supposed to give your MagLite the option of 100%, 50%, 25% brightness, plus strobe mode; problem is, their 100% is more like 75% — the switch itself eats up a significant amount of juice. And it's a bit on the delicate side, too; not what you want when you're out in the woods.