A really clean redesign by the best software people on Earth. In my opinion anyway. Why? You Might ask...

I'll tell you why.

1. Open Source
2. The Best Free Software Around (Thunderbird and Firefox esp.)
3. Actually following standard unlike IE (Microsoft)
4. They Rock

You Shouldn't need any more reasons to get Firefox and ditch shittIE. Incase that doesn't convince you:

1. Tabbed Browsing
2. Popup Blocking
3. Virus Blocking
4. Excellent Extensions (Bookmarks Synchroniser & Developer)
5. And More