Just a few points that don't seem to be covered in the more 'mainstream' background guides:

 1) The roads in much of Ireland away from the Dublin hinterland, particularly those on the West Coast, are pretty rough. If you're hiring a car, go for a French make, they handle rough roads well. Conversely, avoid German models (Germans don't do rough roads!)

 2) Many towns on main routes don't have bypasses and are real bottlenecks.  Add this to the state of the roads and you can easily take 25% longer than you'd think for a journey.

3)  There are very few roadside diners or eating places focussed on motorists (and the ones there are are pretty poor).  In the towns you'll usually find decent eating places, but out of town you're reliant on pubs.  Unfortunately there's nothing on the outside of the average Irish Pub to give any guidance as to whether they're a) open and b) serve food (if you see a sign saying 'food served all day' or similar, don't rely on it).  Good advice would be don't plan on eating unless you're in a decent sized town.

4)  Driving standards are generally pretty good - people are courteous and the only problems you might get are from other tourists (or perhaps a farmer on his weekly visit to town who's more used to driving a tractor ...)

5) In Northern Ireland the roads are a lot better - but the petrol is a lot more expensive.

6) Places often have more than one spelling of their name - even on road signs!

7)  For some reason Tourist Offices are often difficult to find and when you get in to them the staff (almost uniquely for Ireland, which is a really friendly place) often don't seem to really care.  In short, don't rely on them. (Again, Northern Ireland is the exception to this).

8) B & B is a good option.  Many hotels are overpriced and impersonal.  On the other hand almost all B & Bs to be good value, comfortable and very friendly.