DFWRaider, very timely topic as I will be making the exact same connection in early April. I'm flying AA 50 DFW to LGW and then connecting with a BA codeshare of an Aer Lingus flight to Dublin. I did transfer once at Gatwick about 4 years ago from a MRS-LGW BA flight to a TWA flight to STL. It was very painless. I just took the connector bus after getting off the BA plane from the North Terminal to the South Terminal. When I got to the South Terminal there was a transfer desk where I checked in for my TWA flight. I did not have to go through any customs or immagration at Gatwick. Is this still the case? Also, I'm not sure which terminal Aer Lingus operates from. I have seen some websites list North and some South. Since it's a BA codeshare I am thinking that I will have to go from the South to North terminal.