A lot of this depends on the age old cost-benefit ratio – If you’ve done a small crime, your PC isn’t worth the crypt-analyst’s time.  Law enforcement can look elsewhere to triangulate your activities.

If  criminal behavior is suspected to have taken place online, a request can be made, with a D.A.’s signature to the ISP/Online site etc.

As much as you’ll hear me howl about privacy, I don’t take for granted that the services I use online won’t just cough up information based on law enforcement whimsy.
Full Disk Encryption is however, still a good idea, especially if you travel a great deal with your laptop – both in the event of loss or theft of your data, and in other scenarios, it simply makes thieving your data less of an attractive opportunity.

If you’d rather keep your data private, take heart: disk encryption is a lot harder to break than techno-thriller movies and TV shows make it out to be, to the chagrin of some branches of law enforcement. MrSeb writes with word of a paper titled “The growing impact of full disk encryption on digital forensics” that illustrates just how difficult it is.

via  The Hacker News