I changed from UA to AC after about ten years overseas and I've been pretty happy so far. With the changes in AC's program this year upgrades are reduced for E's, but I still prefer AC's economy class product to UA, LH (747), US, LX, or CO TATL. Only problem is that YYZ is a PITA to connect in, at least going to the states from Europe. Other issue is that although AC's *G threshhold is only 35K, intra-Europe flights on *A carriers don't garner much, for example, full-fare Y on LH only gets 50% when credited to AC!