Some say he did, in fact, reach the shores of the New World since Columbus researched Brendan's legend when planning his Western route to Asia.
In the 1970's, adventurer Tom Severin, attempted the same journey using a coracle similiar to that of Saint Brendan.
To early mapmakers, it would seem logical that Brendan would have sighted Hy Breasal, an island in the Atlantic west of Ireland. Found on maps from 1325 to 1513, Hy Breasal was said to, according to Celtic legend, only appear at sunset, shrouded in mists. The Celts viewed it as a 'blessed stormless isle, where all men are good and all the women pure and where God retreats for a recreation from the rest of us'.
In addition to this mythical island, these same early maps would include St. Brendan's Island as well, which some believe was merely the tip of a pre-Columbian iceberg: North America.
The legends of these islands endured so long that it wasn't until the 1870's that they were finally removed from some Admiralty charts.
I do wonder, however, if such a place actually existed. Can, in a fit of tectonic rage, the ocean swallow an island? Perhaps as the oceans rose after the last ice age, the once very real Hy Breasal sank into myth...