I haven't tried Prof's beer yet, but I have been drinking my share of Terrapin's IBA since we now get it in bottles. It is a deliciously fantastic beer. I also brewed a beer similar (see recipe drop-down) from Mike McDole (Janet's Brown Ale in BCS) that is an American Brown with around 65 IBUs and dry hopped (I didn't dry hop mine, but 4 other people in my club have made this and have dry-hopped - truly excellent).
The nomenclature suggests that it is a cross between an IPA and a full-bodied brown ale. You run the gamut with the hop characteristics in bitterness, flavour, and aroma. However, the chocolate and crystal malt cuts through nicely - it is wonderfully balanced. It is still easy drinking, however.
That said, I have an issue with the Dogfish Head IBA. This may stem just on my own personal tastes, but they use a touch of roasted barley in theirs, and to me, it comes through too much. It adds this stout-like roast to it, albeit subtle, but I think sticking with just some chocolate is better off.
