Nice
Learnt about State machines at Uni this semester, and when combined with inter agent messaging it certainly makes creating AI a lot easier and logical.
The plugin needs some polish tho, as Ashley and a few others have said the text should say 'On State Activated' not 'On state false to true', just makes things easier to read.
Theres heaps of stuff you can do to a FSM to make it more advanced, such as having a 'state stack' so you can revert to the previous state, and then theres non-determininistic state machines where you have a 50% chance of doing one thing or another...but really I think that could be done with construct events anyway.
Also incase you wanted to change the icon I made you 2, but you dont have to use them:
<img src="http://dl.dropbox.com/u/939828/ICON.bmp">
<img src="http://dl.dropbox.com/u/939828/SICON.bmp">
I'd also recommend maybe making a behavior version of this as well, although people can just use containers to achieve instancing