Nobody here does, according to the fuel logs:
EcoModder Fleet list - EcoModder.com
But we have a handful of people above 40lmpg with automatics:
EcoModder Fleet list - EcoModder.com
I think that's partly because you can hypermile a manual better to get a larger % over EPA. It's also because the kind of people who feel the need to get >50mpg are attracted to stick shifts and hybrids.
50mpg is a tall order for a four-speed torque-converter automatic, especially if you can't EOC or P&G. You could do it with a boat-tailed SL2, or with a car like the upcoming Fiesta: direct injection, tiny displacement, automated manual transmission. Or a 10 year old hybrid.