PGP FREE: I would think the Windows XP version runs fine on 7 & 8 as well http://www.pgpi.org/products/pgp/versions/freeware/
PGP COMMERCIAL: http://www.symantec.com/encryption
I think it *does* have all the functionality most people need, but the free version is not quite as user friendly as most people are used to. I never tried the commercial one.
I don’t know why people that need encryption don’t use it more. For me, I don’t really need it and figure its use would raise all kinds of red flags, so that’s the trade-off.
The free version for sure, if obtained from a reliable source and verified does not have any backdoors.
It's still out there - the problem is less its availability and more about its utility - in order to be useful for point-to-point communications, both sides have to actively engage in becoming part of the ecosystem, which means as long as relative few people use it, relatively few people will use it (a "critical mass" issue, essentially).
The PGP algorithms are also fairly slow, so they're really not particularly good at doing something like encrypting data on a disk - for that, you'd want to generate a one-time random key, and then use PGP to encrypt the key so that you can recover it later. (Even point-to-point does this, creating a session key that is encrypted with the actual PGP algorithm, rather than encrypting the entire message with PGP encryption.)
And, of course, none of that deals with the fact that all of the data exists in unencrypted forms at certain points in time. With email, for example, the sender composes in plain text and converts to encrypted while the recipient receives encrypted and converts to plain text - the transmission itself is protected, but if either endpoint is compromised, it probably doesn't matter.