The Maps API ToS here:
http://code.google.com/apis/maps/terms.html
will help. Basically they do say that they may decide to limit or throttle your requests to the API at any time at their discretion. You get a personal, worldwide, royalty-free, non-assignable and non-exclusive license.
It may be used for personal or commercial, with the exception that if it's used by a US Government department, there's a separate ToS for that too.
Essentially it's up to you to use for what you will, but their ToS gives them the legal right to kick you out or change the terms at any time. Although I've yet to hear of a case of that actually happening.
