Longhorn, replaces Windows XP Home / Professional
Blackcomb, replaces Windows .NET Business
Effectively they're pretty identical underneath.
Both using Windows NT 5.4 Kernel, running on XNA & Avalon: which is a combination of DirectX 9.1 and .NET Framework 2.0
What it offers everyday people over Windows XP is just really what you see on the surface. Originally Windows Longhorn, was destined to be a 100% .NET Windows.. however, there are an aweful large number of problems that have crept into 'backward' compatibility. This is why there have been 2 designs on the go at once, there was a worry over feasibility of Compatibility with the new technology... So unfortunately the end-result is a Windows XP upgrade more or less.
About what Windows Millennium is compared to 95. A bastardisation of both technologies in order to force compatibility until the market is ready to stand on it's .NET legs.
You'll find the exact same thing in the MacOS X.1, that is due for release sometime at the end of the up-comming year.
However on the part of bloat. You are *still* looking at additional multi-platform capabilities (just not to the degree originally hoped), much smaller executables, more stable executables, more reliance on Libraries rather than in-line code.
As alot of what is being offered really will mean nothing to the pc-illeterate amongst us, what Microsoft have done is added visual effects, customisation, etc.. something people understand.
People understand, 'Instant Internet Access', 'Cloth Effect Desktops', and a-like.
You just say 'Avalon' to someone and they'll probably think 'King Aurthur'
Generally speaking if you've ever seen i-Robot, just think of the people as Will Smith; and Microsoft technology as Dr Kallum.
Techno-babble is all well as good, but lost on those who only understand plain english.
If you want to know what it technically adds to the series then Microsoft have an entire website and developer site dedicated to thier new OS and technologies behind it.