Security is always a cause for concern, whether it be with online banking or simply ordering a Domino's pizza. Passwords used online for applications or services are no different, especially with the amount of cyber crime occuring since the boom of the world wide web. Google have published an article on their blog outlining recent attacks being made on Gmail accounts and how users can protect themselves further.
One way to further protect your email account is to use OTP (One Time Password) via the web interface when logging on across multiple machines, networks and/or locations. For your Windows Phone (and other devices) you can use application specific passwords, which are password that are randomly generated and are used per device. You don't need to remember it and it doesn't affect your main login credentials. Think of it as an access key your device requires to be able to gain access to your account.
Check out the video after the break for the step-by-step walkthrough on using two-step verification and creating an application specific password for your Gmail account on your device.
While the demo is ran for the iPhone, the WP7 setup is just the same. To skip right to the application specific password in Gmail, watch from 2:30 onwards.