Firstly, here's a link to the slides etc. Thank you to everyone who came along last night and apologies for my ListView problems. I've been trying to recreate them this morning and all worked fine in a new ASP.NET 3.5 site I created. My suspicions turned to a reference in my demo site and sure enough there was a reference to both System.Web.Extensions 188.8.131.52 (the current version) and 184.108.40.206 (the version for the ASP.NET 3.5 Extensions). How that got in there is a mystery to me, unless I inadvertently added an ASP.NET 3.5 Extensions item to the site (which implicitly adds the reference) and deleted it.
That's quite plausible but I must have done it yesterday afternoon while testing the demos and then zipped up the problem into my demo "saved state". The problem is easily resolved by removing this reference - something I should have thought to have done last night but often the obvious doesn't easily spring to mind with 200 people watching your demo fail... 🙂
I shall go and fix up my "saved" version to make sure this doesn't happen next time!
I would also point you to my blog entry on Some ASP.NET 3.5 ListView Control Examples so you can see a few examples of the same data rendered in different ways in a ListView control and download the source.