Here is the method:
1) Use del.icio.us API to extract your bookmarks linking to youtube (http://del.icio.us/help/api/)
2) For each entry in the list, call the downloader script on the url.
3) Optionally convert the video to a better format than FLV (http://www.catonmat.net/blog/converting-youtube-flvs-to-a-be...)
Easy :)