For mobile apps (Android, iOS), there currently are no quotas:
The Google Earth API, and native Maps APIs for mobile platforms such as Android and iOS are not affected. Use of the embed feature of Google Maps, and other Google products that offer an embed feature that includes a map, are not affected by these limits."
For other use cases (desktop apps, web services, web sites, etc.), there is still free quotas to use for Maps, only when you exceed them (and if they are enforced), you'll have to pay.
Please check out the section about usage limits in the Google Maps API FAQs for detailed, up-to-date information and pricing.
From the Google Geo Developers blog:
However no site exceeding these limits will stop working immediately. We understand that developers need time to evaluate their usage, determine if they are affected, and respond if necessary. There are three options available for sites that are exceeding the limits:
[...]
We will also provide at least 30 days notice on this blog before enforcement of the usage limits and billing for excess usage begins.
[...]
We will then start billing excess usage to your credit card when we begin enforcing the usage limits in early 2012.
Again, please read the full blog post for all the details.
