[renegadedev]

From the OSM home page: "We started it because most maps you think of as free actually have legal or technical restrictions on their use, holding back people from using them in creative, productive, or unexpected ways."

To me, this is the biggest issue using other mapping services. T&Cs can be a real pain - API usage restrictions, data usage restrictions, quotas, licensing.

Mind you the restrictions themselves are not the big deal but the fact that most major mapping providers don't make these restrictions clear enough - you have to sift through the terms page in most cases and read vaguely worded "legalese" to figure out if what you're attempting to do violates their terms of use.