Show HN: Put “GIF” in front of any YouTube URL and hit enter
Great job with this.  Very useful.  The only issue I see is that Google may sue over domain/trademark issues.  Facebook has done this to many sites for using "fb" in their domains.  While you're getting lots of attention, you may want to offer a browser plugin/extension/bookmarklet that interfaces with the site (have the bookmarklet use a domain less likely to be contested) so that you can keep momentum going if they happen to take your domain.