Finally we have a programmable persistence engine for our browsers. Thank you, Googleplex.
Here's what I want next: more scripting languages. Obvious choices being python and ruby. Whatever happened to this? Slingshot would still have a slight advantage over such a contraption, as Slingshot has some additional desktop integration features that browsers don't currently have. It also has the advantage that it's not running in an application shell designed for browsing the entire web; there's no time machine (back button).
There's also Adobe Flex/Apollo to consider, since they will also have an embedded database available. On the language front with Flex, Adobe recently made an ActionScript Virtual Machine 2 (AVM2) Overview available. How long before someone ports some languages to that VM? Especially since dynamic languages like python and ruby are a fairly natural fit to the AVM2 engine (compared to the JVM anyway), and the AVM2 engine will likely be the most widely deployed VM in the near future (it's included in Flash 9).
The one thing I've been most excited about given the rash of new client products available, is that we've finally got a new "browser war" on our hands. Competition is fantastic; it's going to be a wild next couple of years.