Yeah there are encryption laws which limit the power of the encryption to be used by a software, mainly I assume so that if the FBI or whatever can still crack it to get info, I would say terr0rist activity would be the main reason, there is always brute force with only takes time In the end, just delete your temporary internet files and cookies regularly and you should be ok. There in IE tools/options ....etc.
If you ever have the worry of your PC being seized, then put in the windows disk and re-install, in the select a partition section, just create and delete it a few times if your really paranoid (may have to restart the install process) then format in NTFS (2k/xp only) a few times too, probably only take a hour or so to get it good.
Data can be retrieve from formated drives, but it is not easy, and you don't get it all and the more you format the less you will find.
As for the whole hushmail thing, it definitley safer to use it, and if they want to use it against you they have to also get a warrent to seize info from the email company you use too and if they wont give it up or there out of country there out of luck on getting emails on you.