believe it or not, guinness is a very light beer. fewer carbs and calories than even miller lite, which for a domestic watered down beer, is the lowest.
i also like to drink beer, but i stopped drinking entirely for a whole week, maintained my other calorie intake, maintained my exercise level, and broke through a plateau i had been fighting for two months. granted, i went from 188 to 184-185, which isn't a lot, but it was enlightening to see the impact.
look at it this way, even miller lite has 100 or so calories per 12 oz. so if you, like me, drink 5-6 easily at a time, that's an extra 600 or more calories each time you drink. that makes a huge difference in weight loss.