A PLB is the only way to get help if no one is able to walk out. Otherwise, you sit around until your absence is noticed and you are reported as overdue. That could take days that you might not have to spare. I bet that guy who got his arm stuck under a rock and had to self-amputate would have loved having a PLB.
Here is a report about a guy who fired up his PLB. Two hours later a helicopter appeared.
http://www.whitneyportalstore.com/forum/ubbthreads.php?ubb=showflat&Number=101398#Post101398Interesting that they advise calling 911. Who to call if there is cell reception has been the topic of discussion before. Some say call the county sheriff first. Only the sheriff can initiate SAR. 911 is mainly for traffic accidents. At least, that is the argument.
Backpacker magazine had an interesting article on how a cell phone can save your life. Cell phones exchange hand shake signals with the nearest tower. Even if the signal is too weak to make a call or send a text, these hand shake signals might still get through and can be used to get your general location.
Also, even if the phone shows no bars, call 911 anyway. Some cell companies block access to rival towers for ordinary calls. A call to 911 will always override such restrictions.