I will give you the answer from a security professional's perspective.
Hard disk encryption is indeed a good feature and it can keep all but the most savvy users out of your data, however something to note here is that is indeed possible to get in.
One method which has been making some news lately is to cryogenically cool the memory module so that it can be removed and inserted into another machine before the memory zeros out. This gives them access to everything in memory including the encryption key that keeps your data secure.
So the short answer is that file shredding is still needed if you do not want others to potentially have access to the data. Even a fully encrypted hard drive still can be broken by a person with the right skills. Just look at Bruce Schneier. He makes a living as a consultant training people how to protect from these kinds of threats. A cryptanalyst could certainly get in and gain access to the data should they have sufficient motivation and enough computer power to throw at the problem.
Another note on many of these encryption schemes. The only truly secure encryption method is a "One Time Pad"... Everything else generally has a mathematical solution which is how they know when they have cracked the code. A one time pad is not breakable with any amount of processing power because it is not a math problem but a problem of knowledge.