I've actually actively started to petition clients to use GnuPG since the HBGary hack, but I agree that it's difficult to make progress. Someone has to develop interfaces to make it usable. This is especially needed for web mail clients, the Firefox extension that used to allow this on GMail is no longer maintained.
I'm not a browser hacker so I'm not sure if it would be easy or hard to get this integrated, but ideally the browser would have built-in support for crypto on designated input fields, i.e., "encrypt this text box" option on right-click. I'm sure it would be hard, but I bet if Mozilla and Google got together and worked out a common interface that allowed Gmail et al to pass information to the browser (like whose keys should be used), this would eventually get implemented and be awesome.
As usual, Microsoft is the biggest roadblock with Outlook. Hopefully if your company is using Outlook it can afford a license for PGP, which afaik is the only complete crypto extension for Outlook.
Actually, though I've dabbled but little, it seems pretty easy to get arbitrary encryption on firefox. For an example, look at the LeetSpeak addon, which provides a bunch of ways to transform text, both in textboxes and on the page. The real challenge I can see is to provide a good interface for sellecting from the (potentially hundreds of) public keys at you disposal to encrypt with.
I'm not a browser hacker so I'm not sure if it would be easy or hard to get this integrated, but ideally the browser would have built-in support for crypto on designated input fields, i.e., "encrypt this text box" option on right-click. I'm sure it would be hard, but I bet if Mozilla and Google got together and worked out a common interface that allowed Gmail et al to pass information to the browser (like whose keys should be used), this would eventually get implemented and be awesome.
As usual, Microsoft is the biggest roadblock with Outlook. Hopefully if your company is using Outlook it can afford a license for PGP, which afaik is the only complete crypto extension for Outlook.