I read some reviews by hikers in the Boundary Waters using Spot and none of their messages got out (they were using it from the trees).  For safety purposes I just ordered the McMurdo Fast Find 210 (it even has built-in GPS).  It is a plb that just came out.  It is half the size and half the price of the ACR Microfix.  It retails for $299 and I bought it for $279.  This is guaranteed to work vs. the Spot which may or may not work depending on your location.  If you pay $150 for the Spot and add $99 for the first year of service you are almost at the same price as the McMurdo.  If you are buying the Spot to send okay messages that is another story but for safety purposes the Spot is going to have to lower prices and subscription costs because nobody will be buying them.