In my experience, it's a nice enough upgrade to Vista, but nothing worth getting overly excited about.
I wish there were more control over the new taskbar, so I could have things like only Firefox WINDOWS show up, not each individual tab. Other than that, it adds a few moderately interesting ideas to the OS X Dock which was clearly the inspiration for it. And IMO, I don't care who comes up with it, a good idea's a good idea.
The improved bootup times are quite welcome, and memory management seems to be improved as well.
It doesn't seem to play nicely with the Dell 5310 printers used at work, but I rarely need to print anything so it's not a great hardship for me.
All in all, it's a nice refinement of Vista, but I would stop well short of proclaiming this as some masterful OS release. I still firmly believe that Microsoft has pretty much hit the technical limit of what they can do with the current Windows code base, and it's time to chuck the whole thing, or at least a very sizable chunk, and start fresh. Smaller, faster, incorporating all the lessons learned since the rise of the Internet age, as well as being more nimble and better able to take advantage of multi-core CPUs along with the increasing multimedia demands of end-users.

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