The Star Market at Packard's Corner has a decent English foods section, although I don't recall if it's Vegemite or Marmite that they have. It may be Marmite. I assume it's a Coke Vs. Pepsi thing, people prefer one or the other?
MY roommate in college from from Australia, we used to offer this stuff to people on our floor just to get a kick out of the reactions. I dont remember ever personally meeting someone that actually liked it.
My British roommate used to have some every morning on his toast, but the appeal of Marmite eluded me until I tried it on a grilled bacon sandwich. The salty yeastiness of the Marmite goes well with the smoky umami of the bacon. But that's all it's good for, I'm sure. ;)