I continue to be fascinated by the Dashboard feature in my new Mac, there is an amazing array of widgets available that extend the functionality of existing services in very useful ways. I have also seen a trend of vendors offering widgets or encouraging their community to develop widgets, as evidenced by this contest that 37Signals ran offering a year of premium service to anyone who developed the best Dashboard widget.
Widgets, of all kinds, are one of the realized benefits of SOA (whatever incarnation you want to refer to) because rather than requiring users to go to you app you are bringing your app to them, and more importantly you are enabling an external community to actually take responsibility for developing useful widgets (and their close cousin, mashups).
I can't wait for enterprise software vendors to get on this bus, however it's not evident that we're even at the bus stop as of yet. Salesforce comes close with their appexchange, but I'm not sure that is full web 2.0 as yet. I have seen some Firefox extensions for SAP, although I would bet that it is a complete mystery to most developers at SAP, and if not, then why didn't someone at SAP write these?