Have you looked at the book "Learning OpenCV", by Bradski and Kaehler, published by O'Reilly? I haven't done much work with OpenCV, but I have read the entire book and it seemed to be a good introduction. A companion collection of examples is available online, consisting of a set of programs that can be compiled and used as a starting point for further hacking. A Google search on the title, happens to yield a link to the full text.
The O'Reilly book is very good to get a grasp of OpenCV but it is a bit outdated as it doesn't include the C++ API. You can still run through the examples but you might have to use Google a lot since a lot of function signatures have changed since the book was written. However the book is worth reading since it also introduces and explains a lot of computer vision concepts, as well as providing practical examples on how to use them.
