I have determined that if you can get someone through the first three episodes of Gurren Lagann, they will hold out at least until eight, and if they see episode eight, they will finish the series. I have also determined that if you can get someone to watch two episodes of Death Note, they will watch at least until the halfway point. I think this has to be indicative of good writing or something, and is one of the prerequisites for a show to be considered a "gateway drug." I've found that Cowboy Bebop succeeds despite this...the way it's plotted, while awesome, doesn't give you that same "I have to know what happens next" vibe.
That said, I've gotten like...five different people hooked on TTGL, whether or not they like anime.
Anyone have good or bad experiences with using a certain show to hook someone on anime, or is there a show that you find its easy to hook people on once they like anime?