[ethinson]

I also only add citrus peel for a post-boil steep. You don't need to boil fruit peel to extract the desired oils. You'll boil off most or all of the flavor throwing it in for a long boil.

Bitter orange is not a very good term for what is more accurately described as sour oranges. Seville oranges--what we're talking about--are more acidic than the oranges we typically find in supermarkets. More like a mix of navel orange, grapefruit and lime.

The oranges we find in supermarkets are almost always sweet oranges which are less sour, sweeter and more uniformly the flavor we think of as orange. You generally don't find these called sweet oranges in the US because your typical supermarket doesn't carry anything different.

Both types of orange peels can be used for beers. I like the flavor of sour orange peel better but I have used plenty of sweet orange peel with good results.

To me it's similar to sweet vs sharp/bitter-sharp in apples.  You wouldn't eat a sharp/bitter apple but they are fine for cooking/cider making etc.  I had read that the bitter oranges are used to make orange liqueurs like Gran Mariner and Blue Curacao, and probably flavorings and extracts as well. 

I used sweet orange peel in my Belgian Wit (which usually calls for bitter orange) and it turned out fine to my tastes.  For a holiday style beer like the OPs I would go with sweet over bitter.  My wife makes a stout with chocolate and orange.  Gonna brew that this weekend actually. 

I'll add to the consensus above and say that it only needs 5-15 minutes at the end of the boil.