1970 Barracuda Owners Report (Popular Mechanics, June 1970): http://books.google.com/books?id=8dcDAAAAMBAJ&pg=PA102
1970 Challenger Owners Report (Popular Mechanics, May 1970): http://books.google.com/books?id=qNgDAAAAMBAJ&pg=PA96
I find those two reports quite interesting. Not only problems that are very familiar to us all, but also fuel consumption reports, breakdown of options bought, age group data etc. Lot of complains about service and quality too. 37% of Challenger owners and 34% of Barracuda owners also seem to think they made mistake and wouldn't buy another E-body. For someone not being even born back then I find it difficult to compare how good or bad they were versus other cars built at that time.
There's a lot more on Google Books. Just use advanced search and limit your search to years you're interested.