In the light of NSA revelations, I'm wondering what are some practical steps to improve ones security. I do realise that I won't be able to defend against NSA/other spying agencies, however as they create so many vulnerabilities in products I use, it's only a matter of time when ordinary criminals will start to exploit them.

Is OS X considered secure enough, or should I switch to Linux?

Is FileVault secure? How does it compare to TrueCrypt?

Which mobile platform provides better security? (I do realise that it'd be best to ditch mobile devices, but it's a rather drastic step for most people).

What software use for IM? Is there any secure solution?