Online Tradeshows

We seem to have gone through several B2B waves of online shows/conferences etc, starting with the all singing/dancing 3D effect some time ago, to the middle wave of it's live 365 days a year to the recent wave of being a Lead-Gen product.

Does anyone have any stories, comments or thoughts about an online event they are producing or have recently produced? Did you get a good reaction from vendors/sponsors - was the turn-out rate good? Did you have to promote the pants off the event? How long did you keep it live - and then did you archive it?