If you want my opinion, a resounding yes!
But, who knows ? Right, Microsoft.
I will save you some time and give you in advance the official anwser: Wait for the Build conference september 13.
This is the only anwser for this kind of questions coming from MS those days, when asking about Silverlight or WPF.
If I can give you an advice, a commercial control library is the only way to go for any serious project developed in SL or WPF.
We learned it the hard way with the Silverlight Controls toolkit.
While sporting the name "Toolkit", those are just code incubator, witch can be unpluged at any moment without notice.
That's surely the case with the wpf toolkit, the people who use to work on it moved away on something else.