One of the best things that John and I did to insure that we saw everything that we wanted to see while in Dublin was the hop-on, hop-off bus tour. It takes you all over central Dublin and out to the tourist sites on the edge of town. We got to see a lot of things that we wouldn't have been able to find on our own.
The Guinness Factory was one such stop. While I can't say that it was my favorite stop while in Dublin, it's just one of those things you have to do while you are there. It is almost a national landmark in Ireland and the Guinness family really have done amazing work in the city by restoring parks, opening them for public use (this was in the 1800s), and their employees are incredibly well cared for. While the tour does not go through the actual facilities, it will give you a look into the process of making Guinness. It also gives a lot of historical information as to how Guinness began and how they grew into such a major company.
A major highlight of the tour is the "Gravity Bar". On the roof of the tour building, about 8 stories in the air, they have built a glass bar with 360 degree views of the city around you. If you would like, you can have a free pint of Guinness and if you aren't a drinker or just don't care for Guinness, a free soft drink. Cheers!