I made my pumpkin ale last night, in the end following the all grain recipe from Homebrewer mag. Simple enough - pale alt malt base, a little Vienna malt (this was my sub for Munich malt), some crystal malt, and pumpkin in the mash. I think it went well, but my gravity was four points below what was predicted - they gave in the recipe an OG of 1.064; I got 1.060.
Pumpkin is probably an unpredictable brewing ingredient anyway - not sure how much sugar it has in it, and it would probably vary depending on which type of pumpkin you had. I may have slightly overestimated the weight of the pumpkin (not making allowances for scraping out seeds, skin, etc). And I finished the boil a bit too early so it hadn't entirely boiled down (because the damn boil was just taking so bloody long, closer to 2 hours than 70 mins!). So, given those factors I guess a gravity four points below what's predicted isn't too bad. I checked other recipes with a similar grain bill and found the predicted gravity was in the 50-55 area, so I guess the pumpkin probably added a good 5-10 points to the original recipe.
The pumpkin's added some distinctive sweetness, a nice orangey colour (a bit muddy at the moment but it should clarify in the fermentation), and.... a little charcoaley taste from the skins. I think it'll make a nice spicy brew.