Prices for fixed price things - dinner shows, buffets, all you can eat - are raised during peak times. The dates for 2011 have not been published, but there are peak dates announced for the dining plan (it goes up then as well) so you could take a guess that it will be the same dates. Check the DDP sticky @ the top of the board (or maybe the DDP subboard) and you should be able to find those dates for the DDP surcharges.
There was a previous post from someone who found out by calling WDW. The dates are not exactly the same as the DDP seasonal dates. WDW doesn't publish them anymore, so the only way to get them is apparently to call WDW-DINE and hope you get someone who knows what you are talking about.
LOL - typical. Well I will be there all next week - I'm taking a wild guess it will be peak! I don't think we have any fixed price things planned though - gee, I just realized I didn't plan any character dining - hope my family gets over it! Oops.