Well, we went to the southern area of Ireland in '99. I read that your interested in the norhtern areas...but I thought I'd throw out my experience to see if it helps any.
We stayed for 7 nights, all at different bed and breakfasts. We did not book them in advnce, insetad around 2-3 pm, we'd go to a tourist info center, and ask them to book us one. We always had somewhere to stay, often times they found one with their first phone call.
Lots of cool castles to see...it's very pretty and green there (greener than anywhere I've seen in america, and I've been to 40 of the 50 states).
Oh, and if your into the Blarny stone...I've heard from the locals that the actual stone was removed from the castle, and replaced with a "copy." The natives like to spit and tinkle on the fake one at night. Just a thought incase you decide you want to kiss it.
Erik Johnson