If you are willing to leave your security in the hands of some third party like that -- and do not think for a moment that you are doing anything else when you use Lavabit/Hushmail/etc. -- it is probably because you do not want your email to vanish like that (and security comes second to convenience for you). Think of the alternatives:
* Keeping your secret keys on your disc. Now you crash it, format it, etc. and lose all access.
* Smartcards -- better not lose it!
The reason people use Lavabit is that they want to maintain access regardless of the system they connect from. Of course that also means that other people can gain access (your security is now reduced to the strength of your passphrase, a classic bad strategy), but Lavabit users do not really care. Hushmail and Lavabit both had headline-making stories about how they handed plaintexts over to the government and did not lose their customer base over it.
* Keeping your secret keys on your disc. Now you crash it, format it, etc. and lose all access.
* Smartcards -- better not lose it!
The reason people use Lavabit is that they want to maintain access regardless of the system they connect from. Of course that also means that other people can gain access (your security is now reduced to the strength of your passphrase, a classic bad strategy), but Lavabit users do not really care. Hushmail and Lavabit both had headline-making stories about how they handed plaintexts over to the government and did not lose their customer base over it.