I'm still getting away with the free keys I created before, and haven't given them a credit card, but I'm sure that door will get closed soon. I suspect that if I went over the $200-per-month free allowance, my maps would stop working.
The definitions are almost impossible to sort out, but I think what we're all using in our skins are Dynamic Maps, so our pages would get 28,000 free loads per month. That's a lot of traffic, but what's not clear is what happens when search bots, including Google's own searchers, hit your site and start calling up maps.
You can set a quota, but perversely, they don't let you set a monthly quota - you can set only a daily quota. So, to ensure you don't ever go over your $200 worth for the month, you'd have to set a daily quota of something like $6.50 per day.
This is a scheme that was obviously designed by a huge committee - it's about 20 times more complicated than it needs to be.
Switching to another map provider isn't easy. Each of them has its own API, which means extensive skin rewriting. And which one to choose? Some of the major sites, like The Weather Channel, have gone to Mapbox, so that one might be worth a look.
It shouldn't make any difference - you're calling the same Google map API in either case. But the domain from which it's coming might make a difference to Google. But who knows? Even the information from Google about this change is inconsistent. In one place, they say that pages will stop working, but in other places, they say they won't.
I gave them my credit card, and they send me a bill with $0 every month. You can follow the traffic on their site. However I'm still concerned, because they can change the limit once they want more money, and one day I might end a paid service I never intended to subscribe. So I might add Nokia Maps too, which is using a similar business model, but their usage limit is much more generous. Or perhaps Openmaps... (?)
Today every company seems to change from the free model to some kind of paid construction, and this might be the end of the golden age of internet.