It's just the look and feel, man. You've definitely got some really good information on there. I liked the technique of extending watermarked videos a minute and a half longer. Although all you really need is to just have your URL in the dead middle of the video (that's where YT gets the thumbnail from).
I would NOT recommend you to have your url in the thumbnail since this will actually turn down your visitors. When they browse thorough the videos and see that your video has a url watermarked on it, they will just think, oh hell yeah another spam video. I actually watermark all my videos from the beginning till end (this is to avoid that someone will downlaod my video, edit part the credits found only at the end and at the beginning as i found at some videos, and reupload it with his credits.) and in the middle of the video i actually take the credits off for 3 seconds. This ensure that the url won't be displayed in the thumbnail.