I read somewhere that the activation rate for 406mhz ELTs is up above 80% now versus around 20% for the older systems. I assume (I know, I know) that this relates to fixed units as I cant see that only 20% of the older units would have activated if they were referring to manual activations.
83% has got to be a fairly large percent of survivable crashes, and rightly or wrongly i still feel safer with a unit that has a G switch with the option for a manual switch on if time permits. As has been mentioned, a gps enabled unit switched on manually before an impact should give pretty good location and get the search process under way in a rapid manner.