If that's your page, a couple of criticisms. First off, governments with supercomputers damn sure can break it. There isn't a cryptographic algorithm around that can't be broken with either a distributed computing network or a supercomputer. Assuming, of course, that your letters are always of some length.
Short messages give the codebreaker a lot of opportunities for leverage.
Secondly, you are only linking to the commercial PGP programs, for mac and windows, which are burdened with substantial legal encumbrances and whose source is unknown and may be secure. If you are a Free-Market. There isn't a cryptographic algorithm around that can't be broken with either a distributed computing network or a supercomputer. Assuming, of course, that your letters are always of some length. Short messages give the codebreaker a lot of opportunities for leverage.