Google's video search engine started to index playlists from YouTube and other video sites. Playlists are mixed with standard video search results, but you'll probably find them on the first search results pages if they're relevant.
It's interesting to note that Google's algorithms detect groups of videos even if they aren't called playlists.
"Our intent is to represent the video content of the internet fairly and accurately. We don't give special ranking preference to videos hosted by YouTube or Google Video, nor do we manipulate search results in any way. We believe strongly in allowing the democracy of the Web to determine the inclusion and ranking of videos in our search results. After determining the content of the video using our spidering technology, Google then combines sophisticated text-matching techniques to find videos that are both important and relevant to your search. Our technology examines dozens of aspects of the video's content (including number of hits and rating) to determine if it's a good match for your query," explains Google.