I have cycled both 800 miles round the coast and 450 miles malin to mizen.
I live in Belfast so my first tour took me down towards Dundalk into the south past dublin and over the Wicklow mountains. I cut down through the South East towards Cork. These few days were fairly boring and mostly carriageway. The good thing is on alot of big roads in Ireland you have a hard shoulder on both sides which tractors use and is generally kept clean.
I went through Cork and then started to hug the coast following each penninsula taking me over the Healy pass to Kerry. Kerry must be one of the most beautiful counties in Ireland. I followed the ring of Kerry going against the flow of the tour busses and then round to Dingle, out past Dingle there is the Slea Head drive which is stunning scenery and roads which drop off into the sea.
From Dingle it takes you over the Conor pass which is tough going down into the lovely town of Tralee. I made my way up from tralee crossing the shannon by boat and cycling up the coast of Clare taking in the sights of the Cliffs of Moher, I spent a night in Doolin to sample some traditional irish music and made my way the following morning through the burren to Galway where i got a bus back to Dublin and then Belfast.
I was planning to cycle form Galway up to Sligo and Donegal then back into Northern Ireland and finally down the Antrim Coast.
The following year i got the bus to Derry and cycled up to Malin head, then over 5 days made my way down to Mizen head visiting some of the same places as i had the year before. Instad of the ring of Kerry this year i went over the Gap of Dunloe, Mohlls Gap and the Caha pass in the one day, this must be the best days cycling i can imagine myself doing for some time.
The real gem is down in the West of Ireland in my opinion, twice ive cycled it and i feel i could do it again this summer and see more of it.
The roads generally are good to cycle, i had more bad drivers cycling home from the bus station in Belfast at the end than i did in the whole 5 days of Malin to Mizen. Generally stick tot he quieter roads.
Dogs can be some trouble in the quieter areas and can give you a bit of a chase.
We really are a nation of friendly people and i never met a single person while asking for directions who wouldnt help, i was sometimes dreading asking for directions as most of the time it turns into a full conversation asking how i possibly cycled from Belfast to Cork.
The first year i camped, i can get you a list of my daily mileages and camp sites which i used, sites in the South ranged from 5-10 euro in peak season, most of decent quality except one in spanish point which was some mans field, he was a camp site/shop/post office/house and he wouldnt take any money off me.
Navigation is easy enough, as i said anybody will give you directions, although some people can be optimistic, i was told once "you go over a bit of a hill and its on the other side" an hour later i was half way into what can only be described as a mountain pass in the pouring rain and still no closer.
Weather can be hit and miss, generally have our best weather in late May-early July, even then its worth packing wet gear.