I have attended SOOOOOO many seminars over the years, it's not even funny. From those that we put on with the AWEs, to the ones that I attended and covered for Klixxx and various webmaster resoruces... I've been to a LOT.
That being said, I have to agree with the general consensus here.... seminars are great for NEWBIES, specific NICHE info (those amateur ones Far-L put on were fantastic... I heard nothing but POSITIVE responses from those in attendance), LEGAL (I've heard JD shout his hellfire and brimstone 100x all across the country, and still see them pack 'em in the seminar halls every damned time) and of course PROCESSING. Those are the biggies.
Others that have been sleeper surprisers were a couple of Affiliate Program sessions where reps revealed a little more than perhaps their bosses wanted them to about the programs (lol), the gay panel @ Phoenix 2 years ago (MUCH was revealed for the first time) and nearly ALL of the seminars from that first Atlanta AWE... damn, that was a good show - great crowd, great speakers, great city... it DOES make a difference!
I still attend and have recently finally started speaking... IMHO it's still worth it to participate in one way or another for MOST of the planned panels. But it does depend heavily on the subject matter, who is speaking and who did the planning.
