It's the end of the summer and we've got a great big old release for y'all. It includes a slew of bug fixes, some API changes (sorry), new features, and some new IDE fun. This new release does require Eclipse 3.6 (the core doesn't, but the IDE does), but that brings with it an easier installation (see below)
IDE
Core
Installation
Unfortunately, you cannot just update if you've already got Eclipse installed. You will need a clean install of Eclipse 3.6. Once that is done, go up to Help->Eciipse Marketplace. Select the Eclipse marketplace (if you haven't). Then search for "act-r". Click the install for the core, then back and select the ide. You can then install them both at the same time.
Once that is done, you are good to go. If you want to stay on the bleeding edge (but even more poorly documented), edit your update sites (Preferences-Install/Update) and change 'updates/release' to 'updates/dev'.