The first of my pumpkin beers that I tried after 3 weeks in the bottles had a similar taste and smell. It didn't seem to have the taste when i bottled it. I'm guessing (and hoping) it will fade over time.
I've been contemplating and researching butterbeer ideas for awhile. I'm nowhere near experienced with building my own recipes to provide much of a comment. The only thing i can add based on what I have read is that the fats and oils in the butter would kill head retention. Otherwise I'm anxious...
My favorite Pumpkin beer is made by Tommy Knocker (I can't remember the exact name right now), I did also enjoy the SA one, but our pumpkin beer choices are pretty limited around here.
If everything goes right I'm brewing a partial mash milk chocolate porter on Friday, bottling on Saturday, and brewing my first all grain on Sunday (Chinook IPA kit from NB.
I pitched into a 1.060 because I didn't realize I was out of DME when I went to make a starter. It took a day and a half before there were any visual signs of fermentation.
I mashed 48oz of pumpkin then added an additional 12 oz at 10 minutes then the spice that came with the kit at flame out. Its still in primary, so i'm not sure how it turned out but the wort tasted like liquid pumpkin pie.