My rule of thumb:<p>If the API contains a version number it its URL, then the developers have considered how people will use their service after they add new features, and it's probably good to use.
e.g.
<a href="http://myservice.com/v1/doathing" rel="nofollow">http://myservice.com/v1/doathing</a><p>Unfortunately, there's hardly anyone doing this. As API's get older and we figure these things out, we should see this getting better.<p>As a side note, if you're interfacing with any API though anything other than a wrapper, then you're asking for trouble.