... is not good. However,
Bar Italia/La Corte - several outlets around the city; you'll get accomplished latte art on top of average coffee.
Caffe Cagliostro & Enoteca Della Langhe, Quartier Bloom - A coffee shop and, opposite, a wine bar owned by the same people. Odd place, great selection of wine for drinking on or off premises. Coffee can be good, but it depends on who makes it and what mood they're in. I've seen the staff have blazing rows in Italian whilst serving customers.
Pasta Fresca, Chatham St. - decidely average restaurant, but two of the best espressos I've had in Dublin were from here. However, the second time I went it was pretty bad - they don't seem to have a dedicated barista.
Ariosa, Meetinghouse Square every Saturday - stall selling decent beans and well-made espresso & milkies. Equipment is very old and quality control outdoors in a damp climate must be a nightmare, but it's still about the best in the city. You can also get nice mexican food from the next stall.