Just came back from Perugia in October 2008 from the chocolate festival. It's held in the old historical center which is stunningly beautiful. I had trouble before leaving getting any English information from the official website so just showed up for the first day.
There were tens of covered stalls selling mainly Italian chocolate of very high quality, in bars, truffles flavored with chilli, coffee,, tequilla, cardamon. There were churros and hot chocolate, dipped chocolate bananas, sachertorte with hot chocolate sauce and cream and chocolate liquers.
There were crepes and flat breads filled with hazlenut spread, white chocolate with saffron, all at over 2 - 3 euros a bar and vry few free samples. There was a huge black and white chocolate chess set by Nuovi and Perugina had several chocolate block sculptures going where the chips flew off and you ate them. It was packed during the day and totally jammed on Sunday. At one point, we ducked down a side street to avoid going back through the crowds. There were huge blocks of nougat for 65 euros a kilo, cremino blocks for 38 a kilo and it all looked high quality, but for a chocoholic like me ( or at least I thought I was) it all felt rather sanitary and seemed a little expensive. Would I go again? No once was enough, but if you happen to be in Perugia to eat or for other reasons, at the time of the festival, yes, it's definitely worth seeing.