Based on the awesome feedback, I have been doing some offline development on EVars plug-in lately. I have added some basic documentation on wiki. Installation is now easy, let P2 do the work to install/update the plug-in (it's a struggle to host update-site with google code).
One of the most exciting feature (Which I can't stop talking about) is value based filtering. Now you can have all the powers of predicate expression, how about searching a map like map//key['@user.*']/.. to select entries matching regular expression user.* ? This update also includes support for relational operators so you can search exactly you want like this //value[count > n] .
I have uploaded OPath grammar for the language enthusiasts (left factored, left recursion free). One feedback was 'experiencing some unresponsive behavior for huge graphs' I have addressed that to some extent by integrating progress monitoring and asynchronous interpretation job.
Thanks for the feedback! Also, for those at EclipseCon have fun with your sessions!