Splendid! Rated 5 out of 5 stars
I was looking for something like YTplaylist.com but native to the YouTube.com website. Thought this might be worth a try even though it wasn't exactly what I was looking for. Aaaand...it's excellent! I hadn't heard of SMPlayer before but it plays YouTube links flawlessly and you can choose in SMPlayer preferences what quality level you want to play the videos at. Consequently SMPlayer caches and plays YouTube videos with negligible hiccups and less system strain than playing them in your browser. Very useful if you're on an older computer or slower DSL speed like me.
I thought at first I'd be able to use this with Media Player Classic or VLC Player, but no, it doesn't parse FLV files to the external media player. The media player itself has to be able to parse the video file from the URL.
Windows users: make sure the path to the player has no quotes.