I have this in the secondary right now. I added a can of pumpkin when I did the grains from the extract kit. I'm pretty sure that wasn't right so I just added a little extra pumpkin pie spice at the end.
So far (based on smell and the tastings from my gravity readings) it is more of a spice flavor rather than a pumpkin flavor. If I were to do it again I'd probably caramelize the pumpkin in the oven then add it to the boil. I don't think I will end up with a bad beer but it probably won't be that pumpkin flavor more people think of. Regardless, it should go damn good with my Thanksgiving dinner!