Mark Kiker the editor of CADDManager.com (and a former KETIV Technologies co-worker) published the results of a June survey that asked the question...
What is the PRIMARY way you receive training?
Not surprisingly, the majority of respondees (43%) said self teaching was the primary method of learning.
Although self teaching/learning is a critical option (and for some the only option available), when it comes to learning Civil 3D self learning is not very efficient.
If you are considering implementing Civil 3D ask someone who has gone through the process to see if they would have been able to have done it without training. Most would probably say, no.
There are plenty of comments in the discussion groups that attest to this point of view, but I am a strong believer of independent confirmation and recommend seeking unbiased opinions.
Click on the title of this post to see Mark's survey results.