I am currently drinking my "Oooh Mommy" porter (see what I did there?), where I took my standard robust porter recipe, added a 50g package of kombu (Laminaria sp.) strips to the boil, then another 50g to the secondary.
Honestly, it took some getting used to, but the more I drink it the more I enjoy it. Would not recommend it to neophyte beer drinkers. Very earthy aroma with hits of of that salty air you get at the beach. Standard-issue porter chocolatey sweetness followed by a wash of salty bitterness on the mid-palate. Very long cigar smoke/espresso-type finish.
Caveat emptor re: bottle conditioning - Carbonation level will be very slight with absolutely no head retention. I attribute this to two attributes of the kelp that I should have taken into consideration, both of which act as chemical monkey wrenches. First, seaweeds are naturally high in iodine content. Second, the tannic acid imparted by soaking the kelp in the secondary (the main reason why the finish is so freakishly long). I think a combination of those two are why a brew like this ought to be kegged if you want a good carb level, even if you are adding a seaweed "tea" at bottling.
Also - don't bother adding this or any seaweed to the mash. While there are copious amounts of polysaccharides and other available sugars in seaweeds, at a molecular level they are immensely long chains. These molecules can only be broken down into fermentable sugars by either intensely heating them to between 212-572 deg F (study done at Hokkaido Univ. in Japan in the mid-2000's), or having them partially digested by genetically-engineered strains of E. coli (biofuels study at Cal-Berkeley released last year).