I feel like until we get to the point where "mom and dad" send each other grocery lists encrypted because it's so easy and convenient to do so, we're not going to see mass adoption. GPG is great but it's meaningless if no one else you communicate with has and uses it.
I've taken to signing my emails with GPG in the hopes that people will be curious enough to ask, having learned that I don't have a hope in hell of dragging them through it if they don't have any interest.
Even then, I know that getting them set up with it is not enough to keep them using it if it's irritating.
I had a message I sent myself a few weeks ago fail verification of the key ... and no indication whatsoever as to why it failed (I accidentally left HTML on for that message and that seems to have been the cause).
Until we give people the tools they need (and "easy and convenient" is the missing part they need), we can't fault them for failure.
I started doing some ground work for that myself but it's a huge project so when Silent Circle started talking about doing more or less the same thing I was planning, I decided to wait and see if their solution was viable. Can't really tell by looking at their website whether or not they've got a service related to what I was planning yet.