Apple has posted iDVD Update 4.0.1 which will upgrade your version of iDVD 4 to iDVD 4.0.1. According to Apple’s Readme, “This update is highly recommended for all users of iDVD 4 and will provide for improved reliability when authoring and burning DVDs.”
More info and download link here.
Sure hope it fixes all those problems with “best-performance/quality” burning and slideshows. Ever since I upgraded to 4.0 I haven’t done any projects for fear of screwing up the finished product.