The two main issues when we've thought of this are:
1) how do you ensure the data is accurate/up-to-date?
2) the graveyard issue where you don't want to show what's NOT on your site. As an example (and I know I'm probably picking on them unfairly) check out GreatSchool's crowd-sourced photos here: http://www.greatschools.org/search/search.page?q=boston%20ma)
The two main issues when we've thought of this are:
1) how do you ensure the data is accurate/up-to-date?
2) the graveyard issue where you don't want to show what's NOT on your site. As an example (and I know I'm probably picking on them unfairly) check out GreatSchool's crowd-sourced photos here: http://www.greatschools.org/search/search.page?q=boston%20ma)