Andre's thread on best instructional gave me a good idea. What are the best bjj seminars you've been to and why? I'll begin (in no particular order):
Soneca: very detailed and will come to each group of people and fix very little details and stay there until you get it right. Also a lot of moves are shown all "linking" together. No gi seminars were particularly awesome combining thai boxing with takedowns to sweet ground moves.
Helio and Ryron Gracie: great system of how to defend attacks from the mount, etc. Their defensive jiu-jitsu techniques are very logical, very simple, but very effective. The only thing I didn't like was that the format was question and answer (even though I asked a ton of questions) - I prefer for the teachers to present information instead of just answer questions since it makes the seminar less random.
Eddie Bravo: great format - 2 hours twister, lunch break, then 2 hours rubber guard. I love the 2 and 2 with a break in between concept. I get bored with even the best jiu-jitsu instructor and start to forget moves if one single session is over 2 hours. Also very entertaining, and very step by step instructor.
HONORABLE MENTION: Rodrigo Mederios, Sylvio Braga, Royce Gracie (got a lot from these)