I was there. It was mainly a Q&A with players about running high level games. There were folks like me who pestered them about issues we've (I've) been having with damage of monsters not scaling to mitigation of players and others who seemed to bring in the 3.5 agenda (why do you publish so many books that I am forced to buy!).
There wasn't really any magic fix given out at the seminar. The game's math seems to break down when you have 7 players at the table, particularly with two leaders who can basically fight through everything. The way to keep solo stuff challenging is throwing in lots of other creatures as well.
There were a few things from DMG2 brought up. They had a copy sitting up there that they flipped through and let us flip through.
I was too busy chatting with Bruce Cordell about "Nightwyrm Fortress" which I'm starting next week. Bruce has written P3, E1, E2, and E3 so he has a handle on encounter design. One bit of news - Orcus, in E3, will have a different stat block than the MM1 based on stuff that happens in the module.
I brought up the issue with stun-locking solos. They suggested houseruling it based on your players (I'm sticking with my Stun = lose a standard, Daze = lose a minor house rule for big baddies).
He said you really need to tune encounters around the specific powers of your players at higher level. Your players will be really good at certain things and you have to build knowing for that.
Bruce reinforced again and again the importance of focusing on the fun of your players first. If they are steamrolling through encounters but having a blast, maybe it doesn't need to be fixed.
I don't have all of my notes here in front of me but I did get some good things out of the seminar. When I dig them up I'll post here about it.