The Quicktime X player in Snow Leopard cannot scale its window smaller than the width of the floating control bar. I often want to watch small movies created from screen grabs, and Quicktime X is useless for this -- the resulting playback is fuzzy, having been scaled unnecessarily.
To quickly view a movie without this restriction, I drag it into a new mail message. The player used in Mail has the old-style controller at the bottom, and plays the movies at the correct size.
[robg adds: Another solution is to install and use QuickTime 7, which you can do with the Snow Leopard install disc (customize the installation to see it). QuickTime X is, for me, one of the major disappointments in Snow Leopard. I'm sure it's a foundation for more to come, but compared to its predecessor, it's a very feature-poor cousin with an annoying and useless interface.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20091215190449614