I can't speak for Mighty Moose (haven't used it), but NCrunch is pretty awesome. After using it for a few weeks, you feel like you've chopped an arm off when you start using a Visual Studio install without it and have to run tests manually or drop to the command line to run mocha tests.
To the 3 separate comments on not using IDE below: I am aware of the flaws and I would never use it in a continuous deployment environment, but it's a good gateway tool to get into the mindset of automation testing before moving on to other methods, such as using webdriver from a unit test framework or building a full blown framework (I'd put PageObjects somewhere in the middle).
There was a point for each of us where we had no used an automation library. I think the IDE is a much more accessible way to get in, play around, learn what can be done, and do some very basic tests than it would be to hand them a library and expect them to be able to code up a similar set of tests.