A few things I learned during my recent trip to Ireland:
Visa credit cars do not cover insurance on rental cars in Ireland, N. Ireland, Jamaica or Israel. Bastards.
Do not pay extra for GPS. Just buy a Tom Tom. The piece of E36 M3 Magellan they gave us got lost for hours and it cost as much to rent as it would have been to buy one. Get a map too.
Do not accept the "upgrade" from the Fiesta to a larger car. Even it is a butterly and sublime Peugeot 3008 Diesel MPV. People don't drive small cars in Europe because they are cheap. Europeans drive small cars because the back roads are the size of a gnat's birth canal. Rent anything larger than a Golf and you will regret it.
Driving on the left side was not as bad as I thought, as long as you have a co-driver. Judging right side clearances are difficult though, I left a lot of rental paint on Kerry's shrubbery. My mantra was like a school yard football game - tight left, wide right.
Shifting with the left hand causes a lot of missed 2-3 shifts back to first gear for me.
Passing an eighteen wheeler into oncoming traffic with a diesel is something I will never ever attempt again.
Do not be that guy who rides a bike on the country roads of Ireland. You will get you and me killed. There is zero shoulder. Don't be that hiker guy either. Mad Max carnage can't be far away.
Irish relatives do not understand the concept of 'no more for me I have to drive.'
There is a reason crazy ass rally drivers come from places like Ireland. The average country mum going out on a nappies run could probably compete in the WRC.
Did I mention that Peugeot was really nice? Too big and kind of ugly but I would love to try a 308 instead of the 3008.
