Are you sure you're on the RTM version?  I did a test WPF project and it never pulled up a .Net 4.0 only item.  I used the System.Threading.Task lib on a 4.0 project, then downgraded it to 3.5.  Soon as I downgraded, it failed to compile.

 

Parallel

 

I know beta 2 had some speed issues but on RC and RTM, on any machine I put it on, it works rather nicely.  Do you have any third party extentions installed?

.For(0, 10, (i) => { Title = i.ToString(); });