They are really quite powerful and very easy to use. We're still fiddling with some internal design decisions, but the API is ready to be tested and knocked on.
This is all very new stuff, so all the usual "it's only alpha" and "won't be available until KDE 4.4 is released in Q1 2010" apply.
(Oh, and please excuse the cheesy introduction; it was a long day and I couldn't help myself. ;)