From the beginning WiX v3.7 was designed to be short release. It adds a couple small features to Burn that didn't quite make it into WiX v3.6 and fixes a number of bugs that didn't fit in the WiX v3.6 release. The largest change in WiX v3.7 is the complete redo of the build system that eschews NAnt in favor of MSBuild everywhere.
- MSBuild-based build system - it's all MSBuild everywhere. Much cleaner, much more robust, much better system to take us forward.
- Bundle self-update - a BootstrapperApplication can indicate to the Burn engine that a newer version of the Bundle is available so that Burn can download and launch that install instead. You can see this feature in action with the WiX v3.7 install itself. Just grab and older build and watch the button in the left corner.
- Bundle reference-counting - MSI and (thanks to a bug fix in v3.7) MSP packages are automatically reference counted by the Burn engine. In WiX v3.7 you can specify a stable dep:ProviderKey for your Bundle and other Bundles be able to reference count it. Great if you want to ship redistributables as Bundles. There is a bug open for WiX v3.8 to make this a bit more automatic.
Not a huge, monster update, but IMHO even better because of that. I'd rather an agile like cadence than otherwise...
I've got a strong feeling that I'm going to be revisiting WiX here in the near future [Insert "Setup and Deployment Projects not supported in VS2012" rant here... sigh]