Microsoft hasn't released a new browser in 5 years, but that changed today. Internet Explorer 7 is out and it adds (finally) many of the features, such as tabbed browsing, that have been available in Opera and Mozilla for years. Microsoft clearly does better when there is competition and the competition from Mozilla has finally reached the boiling point and caused the giant to react.
I've been using IE7 for the last 6 months and I heartily approve it as superior to IE6 in both utility and security. Newer websites are already starting to optimize for it. It already possesses 7% of the Flares market. If you're running Windows, you would be well-advised to start enjoying your copy today. (Disclaimer: Firefox, which is very close to releasing version 2.0 officially, remains my favorite browser, on Windows, Mac, and Linux.)