I'll pick off an easy question: The stopwatch is for durations. If you frequently have short blocks of time available and think "do I have any short actions I could handle right now?" then this is for you. As you create your actions, fill in a time estimate ("20 minutes", "1h", etc.). Then when you have this block of time you can group your actions by how long they take and quickly see that you have time to "order food for party" but not "call chatty Aunt Agitha".
Here's some stuff about dates:
http://forums.omnigroup.com/showthread.php?t=3600
You can find some keyboard shortcuts just by looking at the menus. Menu items that have keyboard shortcuts will list them there. Also, we've borrowed a lot of shortcuts from Outliner, so grab Outliner's list (in the Help menu) and see which of those are working.
Your selective iCal syncing request is a popular one. We're pondering how best to approach that.