As you're probably aware there's lots of goodness going into Longhorn, it's far from being a minor upgrade over XP. While we wait for the LH Beta I'll whet your appetite for information by pointing out some publicly discussed items that may seem intuitive but will have a dramatic impact on your PC experience.
For instance, while it isn't exactly new and has been *discussed* since Windows 2000, one new feature for LH is LUA ("Limited User Account", or some folks have called it Least-Privilege User Account). To sound like an insider, pronounce LUA ('loo-uh').
If you're a power user or you work in IT then you know the scenario:
Mom and Pop run as an account in the Admin group because they need elevated privileges to install some free app off the internet or need to install an ActiveX control. Of course, that app is also installing a virus or malware in the background which wreaks havoc on your system because it's running with the same privs as the user. Doh!
A lot of work is going into the effort to not just isolate apps, deprecate user groups and limit an application's privileges independently from the user...oh no, that would be too easy. Read this for more:
Here's a white paper on "Security in Longhorn: Focus on Least Privilege", discussing LUA basics and the 'asks' of application developers on how they can play nice with LUA.
And a slide deck from the '03 PDC discussing LUA called "Building Secure Client Applications in Windows Longhorn" (PPT)
And if you want to ask me "How will LUA affect our embedded devices?" I'd say "Ask me at the Embedded DevCon in May." <grin>