I wish there was a fullscreen mode...
However, Mega Zoomer does a pretty good job as a workaround.

Changes, via google translate:
Version 3.1 (2007.11.4)

* 「タイトルで検索」メニューの追加。 "The title search," added the menu.
* 新規ウインドウをフローティングウインドウにする設定を追加。 New window set to add a floating window.
* 検索用 URL をユーザーが設定できるようになった。 Users can search for the URL you can configure.
* Dock のアイコンにビデオの URL をドラッグして開くことが一部できるようになった。 Dock icons in the video URL to open it and dragging it to be able to part.
* YouTube の仕様変更に対応。 YouTube in response to changes in the specifications.

Over the last weeks, Tuboy Juego is unable to download the FLV files.
Maybe YouTube has made some changes in the website. And probably the application needs an update.

To play downloaded videos in a borderless window, check out NicePlayer.
(Command line mplayer works also quite nicely, but it has title bar.)

Nice and clean interface. Takes less spaces than the youtube widget, making it better to have a video on screen while doing something else.
An interesting option to have would be to make the window borderless.
Thumbnails in search aren't necessary, because it can nicely work with Safari.

There's just one thing that I would like to have in the search: the time of each movie. I suppose it won't be difficult to add this feature, 'cos each YouTube movie has this information.
Otherwise, this is just great! Nice interface and it works very well.
I had tried Tuboy Juego when it was in its early ages and... it was a disapointment. But this new version is excellent!

oh man this is sweet!