I've done 1 pumpkin beer, a partial mash where we mashed cubed pumpkin to try to avoid the hassle of the canned stuff (which I imagine means we didn't get all the sugars out of it we couldhave, but clean up was easy). My understanding is that the starches in pumpkins must be mashed to be fermentable.
I used whole spices rather than ground spices, and was very conservative: 2 cinnamon sticks, 5 allspice berries, and 5 whole clove spikes, 10m before the end of the boil in a 5 gallon batch.
Pumpkin flavor wasn't extremely evident, spice flavor was present but varied greatly depending on whether it was bottled closer to the beginning of the batch or the end. I'm guessing the spices settled to the bottom of our bottling bucket and more made it into the later bottles.
This beer took a long time to carb, and the spicier bottles were less carbonated than the not-as-spicy (the spices probably inhibit the growth of the yeast; I know this can happen with baking).