Getting better and better...
A well setup video link to a few people who might not be able to join in person (Gavin, Jeff, Julian,...) would also be great!
As for detractors: maybe someone from the
BVDW (German organization representing interests of companies in the digital world - claiming: "We are the net"). They had a very critical press release back in June, basically warning every consumer in Germany to use Bitcoins because they have the potential to sustainably damage society as a whole.
If you can't find anybody else, maybe even just an articulate (local) economics professor who opposes some of Bitcoins fundamentals.
While we're at it:
please have a panel discussion - especially if you find a good detractor! Panel discussions (with a good moderator) are IMHO just the perfect format for such conferences.
Apart from that, I second the suggestion to have a microphone ready for the audience or a moderator repeating their questions and please schedule enough time for Q&A.
I'm really looking forward to this event and its great to see it in such capable hands!