In general I’m only using ATMs, but all my ATMs are at branches, no need for interlocking agreements, no worries about fees, and if I actually need banking there it is. Also the presence of the bank makes it easier to know where there’s an ATM, I have no idea what ATMs in the world were co-operative with my CU or where they were, if I see a Wells Fargo sign I know immediate there is an ATM I can use.
...or you just go to any 7-11 or look up the co-op machines on your PDA. Not that big of a deal, even when traveling.