Google today announced Chrome Frame, a plug-in that selectively upgrades Internet Explorer without breaking existing sites. Think of it as working like Flash, but for open web technologies, replacing Internet Explorer’s entire rendering engine for sites that include a single meta tag indicating that they would prefer to use Chrome Frame rather than IE.

So why is this a good thing?

* Remaining IE users (especially IE 6) are unlikely to upgrade because they have apps that don’t work in other browsers. This allows them to get the best of both worlds when Chrome Frame is installed, with fast performance and better features for sites that take advantage of this plug-in.
* Open source and open standards, so it’s unlike Flash or Silverlight, yet still very convenient.
* For users that blindly click “yes”, this is a great way to upgrade them from Internet Explorer, finally, without taking away their “Big E” or having older sites break on them.

Again, this is targeted at people that cannot or refuse to upgrade from Internet Explorer. Obviously Google has a few hurdles to overcome to make this technology completely relevant:

* Supporting older versions of Windows, where older versions of Internet Explorer are more prevalent.
* Convincing IT departments that presently lock down the version of Internet Explorer that installing Chrome Frame is ok.

Even with these obstacles, this is very exciting news for the future of web application performance and ending support for Internet Explorer 6.

Congrats to the Chrome team and Alex Russell, SitePen alum and Dojo Toolkit co-founder, on this great announcement!