Actually using it on one of our WPF .NET 4 project, after 2 hours of using it so far looks looks pretty solid, with pretty good tooling support in VS 2010.
One caveat, the Package Manager Console is kind of neat, but seems to be inferior to nuget.exe (especially when creating new packages).
A very solid, newer (may 2011) in depth video on use and features of nuget get is on channel 9