The rules have been relaxed to some degree over the last few years, but they're still quite strict
In order to register a .ie domain name you don't need an address in Ireland
However you would need to have a "link" with Ireland
So if you were exporting goods or services to Ireland, for example, you could qualify
Also the registry is very strict on who the registrant is ie. you cannot register the domain to yourself for a 3rd party beneficiary. So if you developed sites for clients and normally just registered domains without paying attention to who the registrant (holder) was you wouldn't get away with it
If you have any queries let me know, though I won't be near email for the next couple of days due to a personal matter that has just come up
HTH
Michele