Totally rumor-mill, I had heard that it was, after being acquired by Yahoo, rewritten entirely in PHP, because that's what Yahoo used, and as a result lost all momentum for new features. However, as I said, t his is total rumor mill, and I cannot claim to know if it's true.
Delicious was written in Perl (Mason) and ported to PHP at Yahoo. The language change had nothing to do with the horrible management and lack of product vision at Yahoo, though.
