A great .NET Rocks! webcast featuring Ken Getz talking about VSTO 3.0.
The VSTO discussion starts at about 15 minutes in. Some gratuitous quotes:
"These folks have just done an amazing job"
"For VS 2008, they've made incredible strides... I think they'll finally hit critical mass with this fourth version"
“Things that were incredibly hard are now very easy”
“My jaw dropped when I saw how easy it is to create an Outlook form region”
“The ClickOnce thing is really really huge”