So far, I love it. Good work! Seems suprisingly fast here after that first run, it's just a little sluggish after a cold boot. Maybe a splash screen (something like in Acrylic, nothing fancy or animated or even in WPF as that is part of the load time)
would be helpful there as some kind of launch feedback.
I'd like to see the controls Sparkle uses in my own apps as well. Some straightforward way to change the visual style would be nice (there may be one I haven't found yet, though).
OK press F1
... you can then look at the styling help
Everyone: F1 is your friend ... pretty much everything is easy to do, just read up the nice and concise help topics!