I used Google Trends to plot search popularity of Authorware, Toolbook, Lectora, and Captivate since 2004. It may not be a direct correlation to sales or interest, but there seems to be some consistency with gut-level reactions for industry positions. Authorware trending down since 2004, Toolbook relatively stable but lower, and a pretty good horse race between the seemingly indirect competitors of Captivate and Lectora. A sample image follows below, along with links for some other interesting plots.
Authoring tool comparative search popularity plots
Obviously, the comparisons depend on having a rather specific and unique search term. I unsuccessfully tried doing a comparison of AICC and SCORM, but things like All India Congress Committee (AICC), Antwerp International Cat Club (AICC) and other AICC's left me feeling like it was inconclusive regarding LMS specifications. Through my work with one AICC (Aviation Industry CBT Committee) I've already seen seasonal variations in web traffic due to All India Congress Committee and election cycles. However, I wonder if occurrence/popularity of a common word (e.g., Captivate) is relatively stable in the common usage and in that case product references might drive dynamic changes to indicate realtive changes.