I know the team has been working hard and new stuff has been developed, so I guess this forum topic has just taken a backseat to the blog and other means.
Anyhow, here's some encouraging stuff I just read about Silverlight 4 Beta:
# Performance optimizations mean Silverlight 4 applications start quicker and run 200% faster than the equivalent Silverlight 3 application.
# Deep Zoom enhancements include hardware acceleration to support larger datasets and faster animation.
# Multi-touch support enables a range of gestures and touch interactions to be integrated into user experiences.
So, perhaps we can look for significantly faster performance plus multi-touch technology!
DISCLAIMER: I am NOT officially associated w/ the Photosynth team, nor do I have any inside knowledge.