Andreas - I can't speak for Jack, but in my environment, we don't use the Rich Client - our users just use the HTML version. However, for testing purposes it makes no difference. For example, one report we have produces 34k rows (with 33 columns) and produces a 4.5MB file. It takes 2min13sec to export to Excel whether I do this export using HTML or Rich Client. We have much larger reports that take a much longer time, too, but still no difference in time between HTML and Rich Client.
I guess at least with Rich Client, it has a 'saving...' bubble on the screen until it is done saving it. This is not the case with HTML.
Thanks,
missy