- You can never have enough power in the conference halls. Never.
- Yes, a four-day conference would be great. Give it a try!
- Make the area immediately outside the conference halls a comfortable place to sit and/or mingle. Having an area for hacking at the other end of the building isn't good enough, it needs to be right there. And close the doors so the talking doesn't distract attendees listening to talks (or the speakers).
- The auction is a problem. It should absolutely not interrupt prime socializing/networking time. Make it a silent auction for the run-of-the-mill items, limit the live part to a half-hour of the big-ticket items, and don't be so desperate for large donations - it's unseemly, exclusionary, and probably raises less money than many smaller donations.
I heard about these from other attendees as well.
However, I want to thank the organizers and volunteers for putting together a really really good conference. I was impressed with how smoothly things went, and I all the attendees I spoke to were highly complementary of the event as a whole.