I’ve always been a big fan of greyish interfaces. And web layouts too. From white to black with few soft grey tones…my favourite.
That said, it is damn hard to make it look likeable. It can easily look washed away, or it could be hard to read.
Kevin Davis’s Le Breeze theme for FireFox suffers not, from any of those. It’s a brilliantly designed theme which resembles old Mac OS look. He has similar theme for Thunderbird too. Great work, Kevin.