Bob,
It’s still available, and with we even put a bunch of work into it for 5.1.1, but we’ve never shipped it as part of the base install (something about licensing or what not). Anyway, you can install Matisse4MyEclipse directly from our Discovery Site by using Help > Software Updates > Find and install… > Search for new features to install…
Then select MyEclipse Disovery Site and you should see Matisse4MyEclipse as one of the options.