Well, there is a general consensus in the OSM community, that we just add geodata about mid- long-term objects.
http://wiki.openstreetmap.org/wiki/Best_practices
But of course, the community is very dynamical and yes there are people who contribute geodata about XXL local events (Burning man, ...) or objects with short lifetime (Xmas markets, ...) but be aware that this is controversial, esp. we lack of a unique time model:
http://wiki.openstreetmap.org/wiki/Comparison_of_life_cycle_concepts
No idea if there are mashups that geolocate events an return the data via public API and a good license. Usually people prefer Facebook, Google+, ... so I guess it's not that easy to crawl that stuff legaly.