They nicely package up public key encrytion and make it easy for the general user. I'm assuming that they are using either PGP or GNUPG on the backend and while I haven't checked it out, probably if you pay them for a premium account you can send and receive encrypted mail outside their system.
Therein lies the downside to it though. It's their system and you don't know what's going on behind the scenes. How do you know they aren't parsing (reading) all your e-mails and chats before they get encrypted? I'm not saying they do that, and they look to be a reputable company. I may be more paranoid than most, but if I feel something is sensitive enough to encrypt, then I want to make sure I'm in control.
Which is why I always recommend GNU PG (GNU Privacy Guard), and on the Windows side, Windows Privacy Tray (which is part of the WinPT -- Windows Privacy Tools project). They're open source, your secret keys are stored locally (not on someone else's server), they're actively developed and have large user communities (always handy when you need help), they work with the software you already have, and (for WinPT) I know the developer, Timo Schulz and Timo knows Werner Koch, the head of GNU PG. In fact, Timo and Werner have did work on GPG for the German government.
Here's a cut and paste of another post I've made here at DU on this topic...
WinPT (Windows Privacy Tools) has just about everything you'll need to start encrypting files and e-mail in Windows. The installer will install both Gnu Privacy Guard (GPG, an open source alternative to PGP) and Windows Privacy Tray (an easy to use graphical front end for GPG that lives in your system tray). WinPT even includes a plug-in for Outlook Express and Eudora E-Mail.
http://winpt.org
http://winpt.sourceforge.net/en/download.php
Enigmail is an add-on for the Mozilla, Netscape and Thunderbird e-mail programs that will allow you to automatically encrypt and decrypt messages as well as exchange keys.
http://enigmail.mozdev.org I didn't mention chat in that post, but the open source free chat client GAIM (
http://gaim.sourceforge.net) has a plugin that will work with GPG so that you can have secure chat sessions. GAIM is able to do (last I knew) AIM, Yahoo chat, MSN Chat, ICQ and many others.
Finally, the weakest link in any security product or procedure (including public key encryption) is humans. Education is the first step in combatting that weakness.
http://en.wikipedia.org/wiki/Public_key_encryptionhttp://www.hack.gr/users/dij/crypto/overview/publickey.htmlhttp://www.gnupg.org/gph/en/manual.htmlNote: I'm not saying don't use Cryptoheaven. If it works for you, that's a good thing. I just think many of us geeky types find it's usefulness a little limited and perhaps redundant as well.
BTW: For questions of this nature you might get more of a response in the Open Source and Free Software Group here at DU. :-)
http://www.democraticunderground.com/discuss/duboard.php?az=show_topics&forum=240