Only in Dublin for one day, staying in the city centre. My wife and I planned on just walking around the city but wanted input about the Hop Bus from anyone that's done it or not done it and wished they did. We have no trouble walking all day, we usually do a ton of walking on our vacations.
Should we take the Hop Bus over walking?
Also, as of now, there is a 60% chance of rain on the day we are in Dublin.
Hop On/Off is the way to go. It hits all the highlights and you can get out and walk at will. Places like Guinness, Kilmainham, Museum of Modern Art and Phoenix Park are a little difficult to get to on foot...with the hop on/off you are taken right there. Plus, the commentary is very good (I recommend the green and cream buses - which are featured in your link) for English-speaking visitors...they have a live commentary that is usually more entertaining).
There's probably a 75% chance of having a 60% chance of rain...in other words, that's a very common forcast. The hop on/off is a sure thing rain or shine.
I agree with Corey about the bus. It is a great way to see Dublin and learn about what you are seeing. There is a discount coupon on my Discounts page.
We just returned from our trip and had a day in Dublin. We took the Hop-on-hop-off bus and felt that was the best deal for a short time in the city. We had 4 different drivers and they were all very knowledgeable and humorous.
The buses I took were the usual "big step" to get up onto the bus. Check this website from which you can download a pdf map of bus lines with handicapped access: http://www.visitdublin.com/disabled/