Paul Stovell has discovered that Windows Presentation Foundation uses its own font-smoothing algorithm rather than ClearType, and from the screenshots he has posted it's clearly (pardon the pun) inferior. (Hope you don't mind if I steal your image, Paul!)

WPF vs Windows Forms with ClearType

This is a bit of a worry. ClearType makes text much more readable on most displays (particularly if you've customized it using the ClearType Tuner). It's a big step backwards if your whiz-bang WPF applications have blurry text compared to WinForms.