I think the basic idea of microformats is solid, but still developing, so some of my issues might be with the format rather than with the add-on. Here are the things I noticed and thought needed improving:
* If I export as vcard, the exported file is called "hcard.vcf", which isn't very helpful and can cause file overwrite issues. It ought to take the fn as the title.
* If I don't set an fn class, but only use the given-name and family name classes, the Operator toolbar doesn't light up. fn should be optional, otherwise I'm forced to hide the redundant element(s).
* If I use the "dtstart" and "dtend" classes in anything other than a abbr element, operator doesn't light up for events. Since my page is a schedule, and the schedule is (appropriately) set up in a table, it seems redundant to set the same data in an abbr element when I could just set the dtstart to the table cell.
* If I add a single event to my Google Calendar, I'm redirected to Google Calendar in the same tab, so I lose the page I'm on. At the very least, a new tab should open, but ideally I should be able to choose the location of my gcalendar as an option and not have to do anything at the Google Calendar site (not sure if that's a gcal option).
* If I have a page with a dozen events, I can export the entire calendar as an ics file. It would be nice if I could rename it something other than hcalendar.ics (maybe the suggested title could be a class, like class="hcalendar venue_cal_concerts", or something) or the user could choose the title. It would also be nice if instead of exporting it and then reimporting it to gcal, if I could "add all to Google Calendar".
I know the developer is in need of financial support to get back to this project, so I'm not expecting overnight implementation, but all of these seem fairly natural improvements, assuming they can be done at the add-on level.