This is not meant to be a thorough report, just the highlights I found relevant related to its recent release.

Versions

• Starter is weak (for netbooks) 32-bit only, OEM pre-install only
• Home Basic is for emerging markets (we probably won’t see it in the US much)
• Home Premium is what most consumers will end up with
• Professional is the lowest version to include features such as Remote Desktop Serving, Domain Joining, and Windows XP Mode
• Enterprise is the same as Ultimate but with volume licensing and they both include BitLocker
• Ultimate has all possible features (of course)

Wikipedia detailed Windows 7 Version Comparison Chart

General

• Supposedly 7 can be installed from a USB drive (without hacking).
• Internet Explorer 8 can pretty much be removed – many parts are integrated into the OS, but the browser can go bye-bye.
• The sidebar is gone but Gadgets remain, and are more efficient and movable.
• There is an overly hyped new taskbar.