Sorry I didn't find this thread sooner... SPOT is offering a $49.99 rebate on the SPOT Tracker until March 31, 2010 (today). I bought mine for $99.99, so I got it for $50... not bad. The service is $99 a year for the basic subscription up to $160 for the full blown tracker package with GOES membership and rescue insurance. The Tracker feature can be had for free (normally $49.99/yr) by using the promo code "Tracker23" when activating your device.
All the information in this thread is great, but if you ride outside of cell service, or worse yet, are incapable of making a call, it would be nice for rescue workers to find you quickly. As a pilot, I chose SPOT over a traditional ELT... if I go down, there is no question where I am. When riding, the the same device is tied to my Camelbak.
The new version (SPOT-2) had some issues when it was first released, but they have them fixed up now. The difference between the two is primarily in size (SPOT-2 is about 60% the size of the Tracker), and SPOT-2 has a couple of additional messaging features and a slightly improved GPS chip. As far as satellite tracking is concerned, both are capable units... Tracker sells for $99 ($50 today) and SPOT-2 is going for $169. Well worth the $$$... check em out.