I suspect that most people listing their visited sites will already "know" how many sites they have visited as they will keep their own list/spreadsheet - so they won't be doing it to find that out. But it occurs to me that there are a number of statistics which the site could perhaps more usefully produce about each person's "visited list". Doing so might provide more incentive for people to "register" their list?
The majority of people bothering to enter their list are going to have visited 100-300 sites I guess with a preponderance in their home continent. That still gives a reasonable opportunity to produce some worthwhile figures about their lists I think.
I could program my spreadsheet to tell me how many natural sites I have visited and what %age of those in Europe etc etc but this site could do it perhaps more easily - particularly as the updates of new sites are done for us each year and, since new statistics can be produced as more information is added to the site.
So as a start the sort of information could be for each person's list :-
Numbers of Natural, Mixed, Cultural and Cultural landscape sites visited in total and by continent.
%ages of each within the Visited list and of the Total list
The most and least "visited site" (as per users of this Web site) in each continent which the person has visited.
The UNESCO definition of "region" is somewhat strange, bringing together as it does Europe and N America - I would suggest that the "classic" definition of continents is used with Oceania being put with Australasia. Islands should be linked to their nearest/most appropriate continent unless they are inscribed as a dependent territory when they would go with the owning coutry's continent.