This is one of the top encryption tools on Windows, and it's great to see it on the Mac. It offers highly secure encryption for file volumes (disk images) and filesystems (not including the boot drive/partition). In my testing it was stable and performed fairly well. (Equivalent to most other FUSE-based filesystems)
Unfortunately, the Mac version falls flat in many ways compared to the Windows (and Linux, in some cases) versions of TrueCrypt. These limitations limit the usefulness of TC, especially compared to other options on the Mac. Specifically:
Hidden volumes are not supported, and therefore there is no standard of plausible deniability. The fact that there is encrypted information and the quantity of it is obvious to an adversary.
There is no "traveler" mode, so you cannot keep encrypted volumes on a portable disk without installing MacFUSE and TrueCrypt on each system you need to access it from.
There is no encryption of the boot drive. However, external drives can be fully encrypted.
It only supports the FAT32 filesystem. Native HFS+ is not supported. So you have to deal with .ds_store files, etc.
It relies upon MacFUSE, which is something of a moving target as it's under active development. This also creates a potential security weak point that the TC authors would not necessarily be in a position to correct.
Given all of this, Disk Utility's encrypted disk images are, in many ways, superior to TrueCrypt. TC is more difficult to use (it's distinctly un-Mac-like) and less widely supported on the Mac.
While the encryption is stronger (512 bit encryption vs. 256 bit in Disk Utility), neither can be readily compromised through brute force. There is also some security in TC being an open-source project. Apple's implementation of secure disk images has not had nearly the review that TC's has.
The one real advantage of TC is that its encrypted disks are cross platform. Or, more accurately, the Mac version of TrueCrypt can access Windows' TrueCrypt volumes.