Mylar remembers what you were doing when you switch between tasks. This is pretty closely related to my second reason, but I think it deserves it’s own special spot.
Not only does Mylar keep track of what you’re doing, it keeps track of it on a task-by-task basis. Here, for example, is what my Eclipse workspace looks like when I’m working on a bug for an Eclipse Corner article (bug 138600).
This bug’s going to be open for a while, so it’s handy that Mylar keeps track of the file that the task is concerned with. When I switch to instead work on a Phoenix bug that’s assigned to me (bug 164658), the views change:
Very handy. Switching between tasks is a breeze. It’s easy enough to just click on the “activate” button for the task, but you can very easily flip between recent tasks by using the drop-down on the task list:
In case you missed it, Mylar 1.0 was released today.
Eclipse Hints, Tips, and Random Musings 
You should try Ctrl-F12, Ctrl-Shift-F12 and Ctrl-F9. But my personal favorite is to use Alt-Shift-N to create new repository tasks.
I don’t use the keyboard all that much myself (I like to keep a hand on the mouse), but I do let an occasional keystroke into my editing vocabulary. I’ll give these a try.
For activating tasks I usually find myself using the Task List too, but I do frequently use Ctrl+Shift+F9 shortcut for Deactivate Task. If you use a ThinkPad laptop F9 is an easy key to remember because it has the Eject picture on it (on a Powerbook the picture is for reduce brightness, which is not bad either). For the meanings of other shortcuts Eugene mentions, if you click the Navigate menu you’ll see the actions listed.
I’ve found it incredibly handy when a coworker comes and says “Hey, can we look at the bug/feature you were working on last week” and I can stop what I’m doing with confidence (because I know I can get things re-opened in a jiffy) and in almost the blink of an eye I’ve got the relevant classes and files opened for the bug in question. It just makes life so much easier!!!
Mik, what I really miss is the task deactivation button on the main toolbar (as well as the dropdown with previous tasks). Strangely, I also happens to have my hand on the mouse at the times I need to deactivate task and still can’t get used to Ctrl-Shift-F9.