I currently use an auto-siphon which works well but with Drew's system I like the idea of not moving the carboy and minimizing the beer's exposure to O2.
The not moving it part is definitely the main reason I do it. I started doing it because I just didn't have anywhere high enough to set the carboys for settling and I really hated a) the danger of moving a full carboy - again b) stirring up sediment that had settled.. So, on with the CO2. It also helped that until 2 months ago I got free CO2!