In addition to @ultrasawblade's comments, there are a couple of other things to consider when evaluating TrueCrypt. One of the main alternatives to TrueCrypt (if you're using Windows) is BitLocker. BitLocker can be configured to authenticate against the TPM in your computer, such that a unique key is stored and provided at boot time without you having to know the password. A recovery password is also provided, but it is typically not needed and can be stored in a secure location.
This brings me to the biggest (IMO) weakness with TrueCrypt: it requires users to memorize and repeatedly enter another password. This leaves users' hard drive encryption vulnerable to the most common attack in the world: password compromise. Either by sharing it with others ("Hey, Bob, I'm not there right now, but just get those files off of my computer. Yeah, you can log in with your username and password, but first you have to enter this one at the black screen with the white text--that password is 'password'") or by writing it down on a post-it somewhere easily readable.
The cryptography algorithms used by both TrueCrypt and BitLocker are fairly strong, and would require a lot of resources, both physical (access to the hard drive) and computational to crack, but I prefer BitLocker because it is built according to the philosophy of "your Windows login should be the only security you need, and your hard drive should transparently boot windows if it is in its original computer."
To be sure, there are restrictions in using BitLocker: you have to be running Windows 7 Ultimate or similar and have a TPM-capable computer. It's not without vulnerabilities, either: the recovery passphrase can be stolen (though it doesn't have to be used all the time, so the risk is lower), the TPM can be cracked (unlikely), or the user's Windows login could be compromised.
For more information on full disk encryption software, check out this wiki article.