I would certainly pay €100-200 extra to get it in a LBS, probably even 3 or 400 more. But the savings are even greater than that; often in the thousands for even mid-level bikes (e.g. €2,350 bike for €1,300 sort of thing.)
Ciaran- you can't buy a Trek online any more, it's in person from a dealer only.
There are also differences between the online shops; CRC just ship the box to you as is but Wiggle fully assemble and adjust the bike (I have bought bikes from both.) And then there are the bikes you can only get online, or not from Irish dealers anyway.