I just put 2 one inch holes in a Oceanic 37 and a few more in a couple of smaller tanks... and then a few more in some frag tanks that I'm setting up.
I suggest a practice tank if you are nervous. Buy a 10 gal from petco, they're like $11 or so. If you can drill that, you can pretty much drill anything as the glass is way thin.
I always use a higher speed with the drill, it keeps it from binding up on the glass and cracking it. I start the bit off on about a 40-45 degree angle and keep it there for about halfway through the drilling.
So far I've put a few hundred holes in tanks, no problems thus far.