Microsoft's RSS team blog has this news.
"IE7 Beta 3 is here! We’ve snuck in some goodies in the feed reading user experience based on your Beta 2 feedback"
If you have previous IE 7 Betas installed you need to know this (from the IE7 FAQs)
"Upgrading Internet Explorer 7 Beta 3
If you want to reinstall Internet Explorer 7 Beta 3 (or install a newer version) you must first remove any existing Internet Explorer 7 beta versions on your system. You cannot install Internet Explorer 7 Beta 3 over previously installed Internet Explorer 7 betas. To uninstall previous versions of Internet Explorer 7 refer to the uninstall directions below."
The IE team blog has more on this.
Max Stevens, Lead PM on the IE team shows some of the UX improvements made for this release.