So, not to bump super old threads or anything, but interesting factoid, as a homebrewer...
BREW magazine did an article on stouts and brewing techniques used by popular commercial stouts.  Guinness is actually not even a stout anymore, it is actually a light lager with flavoring added after the fact, hence the super watery mouthfeel.  How people can say it tastes thick is beyond me, the mouthfeel kills guinness for me, so nasty.
If you are looking for some good darker brews, I highly recommend sammy smith oatmeal stout, mackeson xxx stout, and for something completely different, Stone smoked porter is great as well.  All are very different styles and deserve a look