We use Login Enterprise extensively, both for load testing and daily performance monitoring. We have two farms, one Citrix and one pure RDS. Currently, our testing is on our RDS farm, but we'll extending that to the Citrix farm shortly.
I'm actually doing a presentation at Amplify that discuss how and why we use Login Enterprise. Also, it's strengths and weaknesses and how we've built a bunch of tools to make it useful to us and at our scale.