It's certainly true that some of the non-compete clauses in employment agreements may not be enforceable. To be enforceable in Ireland, the clauses need to be reasonable as to (i) scope (i.e. what are they trying to stop you doing) (ii) geography and (iii) time.
E.g. If you worked for Microsoft and they said you couldn't work for anyone competing with Microsoft anywhere in the world for a year, that would probably be unenforceable (MS being so huge and having so many competitors, for one thing). But, if you held a sales position in a local estate agents and they said you couldn't work in a sales or mgmt capacity for an estate agent within 25 miles of your employer for 3 months after termination, that would probably/possibly be enforceable.
Unfortunately, there's no bright line in these things as it depends very much on the industry you are in and the position you hold.