If you have never watched one of Gojka Adzic’s presentations, you really should. This one is about 3 months old and in the first part is one of the best discussions I have seen on why so many projects and requirements efforts, including those that are “Agile”, fail to deliver value. He also some valid comments on Business Analysis at around the 32 minute mark, and provides some suggestions on addressing some common pitfalls with Impact Mapping starting at around the 37 minute mark.
In my opinion, this one video has more value to Business Analysts than any webinar I ever attended. If you have the time, give it a watch.