CalConnect.org has just published the RESULTS FROM FIRST RECURRENCE QUESTIONNAIRE
The results further validate the CALSIFY proposal to remove recurrences rules as they stand in RFC 2445 iCalendar. With respect to VEVENT, only 42% supported recurrence rules in general and the number quickly falls below 15% (2 responders) when adding some of the tricky parts, such as, recurrence id, time zones, and ability to cancel a single event within a recurrence.
I was disappointed that the survey received only 19 responses and that it did not include whether the responses came from commercial, custom, or open-source applications. In addition, it did not state if the same vendor may have responded for different versions of their product. I would also be interested to know if the market share covered 2% or 98% of the market.