I'll be giving a presentation at the upcoming XML 2006 Conference in Boston on Tuesday December 5th at 1:30pm: The Essence of Declarative, XML-based Web Applications: XForms and XSLT.
I've been doing some hardcore XSLT/XForms development over the last 2 years or so and have come to really admire the versatility of using XSLT to generate XForms user interfaces. Using XSLT to generate XHTML from compact XML documents is a well known design pattern for seperating content from presentation. Using XSLT to generate XHTML+XForms takes this to the nth degree by seperating content from both presentation and behavior (The Model View Controller design pattern).
The icing on the cake is the XPath processing capabilities native to both XSLT and XForms. It makes for easily-managed and relatively compact applications with very little redundancy.
The presentation doesn't cover this, but the XForm framework also includes transport-level components / mechanisms that are equally revolutionary in how they tie web clients into the overall web architecture context very comprehensively (Rich Web Application Backplane has good coverage of patterns to this effect). I've always thought of XForms as a complete infrastructure for web application development and AJAX as more of an interim, scripting gimick that enables capabilities that are a small portion of what XForms has to offer.