I used the HOHO bus on a trip to Dublin in around 2009. There was a new company operating at the time for a total of 3 HOHO companies, and I got a great deal for 72 hours since they were the "unknown" company. I used them for the initial orientation to the city, then for trips to Guiness, Kilmainham Gaol, Trinity College, the GPO, St. Patrick's and Christchurch Cathedrals. I used the bus in the evening to attend evensong at Christchurch and for transport to restaurants near their stops. Often, I was the only passenger on their bus, and so I got a personal overview of Dublin Georgian architecture with a young tour guide/architecture student and a discussion of Irish literature with another tour guide. He recommended a few authors I had never heard of (Sheridan Le Fanu, Niall Williams, Kevin Barry), whose books I've enjoyed immensely. I'd rate it a great experience, but I was also housesitting at the time, so I had plenty of time to spare. I generally use the LUAS or walk now, as the HOHO can be crowded and involve more waiting. But if you feel like trying it, go for it!