Release notes can as ever, be found in the Knowledge base!
Thanks to Pawel Frankowski of Gavick.com for pointing out this notice that has been appearing from time to time
The EmailAsUserame plugin does not yet work with Joomla 1.6. Do not install it on a Joomla 1.6 Site! We're working on compatibility at the moment, and should have a Joomla 1.6 Compatible version by 15th January February.
EDIT: You know when you look at something and you think "Yeah! No problem!" But it actually turns out that its more of a problem than you thought? Well, this is one of those times! We're trying to get to grips with Joomla 1.6 new plugin API, and without any obvious documentation, its proving harder than we thought! more updates to come!