It was my pleasure here at PDC to meet Dave Glover. Dave is one of Developer Evangelists from Down Under (Australia). Dave showed me this cool 5.0 Smartphone app he's written for collecting informal surveys during presentations, meetings etc. Participants can SMS their vote to the device and it records and tabulates the results.
It's written in .NET Compact Framework 2.0 and uses new managed APIs in Windows Mobile 5.0 for intercepting incoming SMS. Interestingly, if you search in VS 2005 help for SMS Interception it'll take you directly to Dave's sample.
You can find more information as well as his source code here