I think Brian's article really sums up things nicely:
http://www.procooling.com/articles/h...trol_met.shtml
Although it doesn't mention the possibility of just using a switch with resistors to get 2-3 desired voltages (like Thermalteke does on their Volcano 7+).
I am not a big fan of the "7V trick" myself but I have done it with no negative effects.