Google Gears is currently a beta product; moreover, it is currently considered to be a developer-only release. When the developer community has had a chance to examine, critique, and improve Google Gears, a final version suitable for use with production applications will be made available.
Google Gears is open source software, licensed under the New BSD license. Generally speaking, this license allows you to embed the Google Gears runtime or API in your software, without restriction. You should, of course, consult a lawyer about licensing issues before choosing to embed Google Gears in your software. There is no restriction on web applications which make use of Google Gears installations on users' computers.
Google is working with a variety of partners to make Gears widely available, and easy for developers to use.
For more information, visit the Google Gears Developers' Site.