It seems like YouTube has added a new format for playlist URLs. You'll find it on search result pages. The ID of the playlist comes after:
list=PLSo a complete URL containing this format might look like http://www.youtube.com/watch?v=hzMtVJTxrJw&playnext=1&list=PL00A3D4ABEAF28FA3
I've added support for this format in bcccc0f7 to YTPlaylistFetcher. You can download the latest version by right-clicking on the previous link and select "Save Link as ..." from the context menu.
