Much of the information on veganism out there appears to be aimed at people just starting out and don't really know anything about being vegan. What is it like to be a "long-term vegan", and how does it eventually affect your lifestyle?

There is a lot of "newbie" vegan information out there, which is primarily aimed at people who are crossing the divide between the conventional non-vegan way of life into a vegan lifestyle. Some people have to do this gradually, while others can jump right in. While some, but not all, will struggle with the transition and may even give up completely, there are many stories from long-term vegans, and how they keep going and stay strong in their lifestyle. 

The following link offers testimonies from long-term vegans, and basically, what keeps them going on the path they've chosen:

http://thevegantruth.blogspot.co.uk/2013/03/a-compilation-of-long-term-vegans-our.html