CloudMagic, a new extension for Firefox and Chrome which is designed to allow super fast search of your inbox, as well as in-window preview and multiple account search was released earlier this week, promising to "revolutionise" your inbox.
The software looks good, and while it requires your password to access Gmail, stores all data locally, so no need to worry about who else might snoop into your inbox. It doesn't actually use Gmail's built in search box, but instead adds one on the top right of your window to allow you to use both.
The indexing service works surprisingly well, and is very easy to setup. All you need to to is drop your logins into the preferences page, and it'll begin indexing. You can add as many accounts for indexing as you like, and the service will index them in one place. I found it particularly handy when in the middle of an email, I was able to search for previous correspondance without having to leave the open page, preview it on the same page, then carry on emailing.
CloudMagic also indexes your contacts, and future versions will index Google Documents, much like the "Search Documents and Sites" lab that is built into Gmail.
On my first run I actually ran into compatibility problems with Firefox 4.0 Beta 3 and 4. Eventually I managed to install it in Google Chrome, but found that because my work uses a proxy, I couldn't use the extension. CloudMagic does support proxies, but only if certain ports are enabled.
Have you tried CloudMagic? What do you think?