I was recently tipped off to yet another Seattle bus tool: One Bus Away, which not only provides real-time bus arrival information for every stop in the Metro system, but does so in a variety of formats. You can use the Web-based interface (which is close to what you can already get from the Tracker Location View), but the real magic is that the information is also available via SMS, Web-enabled handheld devices, and—most important to me—any mobile phone.
I have One Bus Away on my speed dial, and I've set bookmarks on the stops I use the most, so I'm never more than a few taps of the phone away from knowing exactly when my bus will arrive. This is a fantastic anxiety-reliever when I arrive at my stop very close to the posted time and am left wondering, "Did I just miss the bus? Or is it running late?"
Bonus trivia: I had assumed that the Metro buses transmitted their locations to the central computer with the assistance of GPS technology, but in fact, it's much lower-tech: They just transmit the current odometer reading. Since buses travel along a fixed route, knowing the odometer is enough to give you the bus location. (Assuming the bus has not diverged from the official route...)
Bonus update: I used One Bus Away just this morning. I was running a bit too tight on my morning schedule, and as I hopped on my bicycle, I called One Bus Away to find out how much time I had to get to my normal bus stop. It was a bit too close for comfort, so I took a detour to a different bus stop (a little further down the route to buy me some more time) and caught the bus easily.