According to this article, 80 percent of Aer Lingus’ transatlantic traffic is now originating beyond the Irish market (dated October 2011):
Aer Lingus, pursuing sixth freedom strategy, seeks trans-Atlantic joint venture | CAPA - Centre for Aviation
Another interesting statistic, according to Aer Lingus' Annual Report 2011, is that 21% of passenger revenues are now generated from passengers connecting from inter-airline carriers:
http://www.aerlingus.com/media/aerli...Report2011.pdf