This release has a number of fixes, but the main one to think about is the breaking change to event raising discussed here:
https://groups.google.com/group/nsubstitute/browse_thread/thread/eda718d5f35d6211
You can check the documentation for examples of the modified syntax (http://nsubstitute.github.com/help/raising-events/). I'm also available to try and help if you run into trouble; just email the list, or email me directly if you have code you can't send to a public list. If you have an OSS project with a public repository drop me a line and I'll see if I can do the upgrade for you (no promises though ;)).
Other changes of note are some big improvements to the way that argument matching works thanks to Anthony. (Unfortunately this is one of those features you'll only notice when it goes wrong, and Anthony has done a lot of work trying to make sure it doesn't.)