Strong bodily reactions are a great way to measure the impact of new technologies.  While many US technical conference crowds like clapping when they see new features demoed, I think the best reaction is a more modest bodily reaction. I'll never forget the time I shivered after seeing Eric Gamma demonstrate the Refactoring support in Eclipse a couple of years ago.  One area of .NET 2.0 that is generating strong bodily feedback is ASP.NET 2.0's support for Custom Build Providers.

First there was Fritz dropping his jaw when he created a custom build provider that took his custom XML metadata file which he dropped into the app_code directory that automatically generated the strongly-typed classes for him.  Tonight I discovered that Kirk Allen Evans had a similarly-sized bodily reaction when he created a Custom Build Provider that automatically created XmlSerializer classes that allows you to drop a schema into the app_code directory and automatically generate the XmlSerializer class.

I'm with these guys: Custom Build Providers are cool (bodily reaction: light goosebumps).  I'm passionate about finding ways of driving application development through the use of metadata files and the Custom Build Providers are an innovative way that ASP.NET provides to support this kind of development.  The only downside I can see is that the creation of these classes is slightly 'automagical' and requires that developers understand what the framework is providing under the covers.  However, I think this initial learning curve is more than compensated for by the productivity that Custom Build providers enable.