Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.
CaveDigital has published a very cool WebPart which makes it possible to preview your published InfoPath forms. After installation of the WebPart you have to add it to a Form Library. Each published InfoPath Form gets an menu option "Preview XML Form" which shows a preview in the CaveDigital WebPart.
Way to go CaveDigital :)