I had this suggested to me for SU just a few weeks ago. Glad to see someone’s done it 🙂
The Saabway Club is located in Italy and they’re the first I’ve seen to employ a Night Panel button as a theme switch for their website.
The normal view (click to enlarge):
Note the Night Panel button in that image (a red arrow pointing to it).
And with the Night Panel switched on….
But maybe it should darken everything and only light up the appropriate area when when you mouse over it (e.g. a forum topic) ……. 🙂