If there is an actual click-through and the license is understandable by a human, perhaps. Usually there is neither, though.

I rarely even know how to look up terms of an API, or that there is an API. If I know the name of the API, I can look for "Google Foo API", but that name isn't always obvious. If I just see a URL with an obvious schema, and I change the HTTP GET parameters to retrieve different stuff, am I allowed to use that in, say, a small-scale art project, or not? The usual internet default is that public URLs are implicitly giving blanket permission to retrieve them, except that retrieval by spiders should abide by robots.txt. Google itself makes heavy use of this ok-to-retrieve default assumption.

If I go to http://maps.google.com there is no license presented to me as a condition of using the service. I can however look for fine print and seek out the link "Terms of Service" of my own accord, at which point I get this: http://www.google.com/intl/en_ALL/help/terms_maps.html

Those terms specifically forbid several things I'm definitely not doing (mass-downloading data, using it for turn-by-turn navigation, etc.), so my first read of it makes it sound like grabbing Maps content in my art project is okay. But then I'm not a lawyer, so maybe it isn't okay.