Can WPF and WinForms be mixed within an application?

Question

Can both WPF and Windows forms controls be used within one application? How difficult or practical an idea is this?

Answer 1

We hosted significantly complex WPF controls in an existing LOB WinForms app. It can be done, but we did have issues (some no doubt caused by the steep learning curve). These primarily had to do with loss-of-focus events not being fired when expected, and also keyboard navigation issues.