For the past few months I've been hearing about the MegaBus service, which recently made it to Minneapolis. A European company with a line of inter-city express busses has set up shop in the Midwest, running a limited selection of nonstop routes between Chicago and other regional destinations in what is clearly designed as a minimal-overhead operation. Booking is, so far as I can tell, almost entirely online and automated. In Chicago, they claim to leave from Union Station, which is true insofar as the bus pulls up to a sign on the sidewalk outside Union Station's entrance; in Minneapolis it dropped me outside the University Ave. parking garage.
On the upside, the ride is quicker than Greyhound's (nonstop, after all), and ranges from 60% of the Greyhound ticket price to practically free, depending on various factors. Also, since there's no depot or luggage check, I could in principle exceed the 50-pound per-bag Greyhound limit, so long as I can still lift my kit into the under-carriage stowage. The ride was far less crowded than I'm used to, but that's probably because the service is relatively new and apparently spreading mostly through word-of-mouth so far. I wouldn't be surprised if they do well, but it would be money prudently spent to erect some awnings to wait under before next winter arrives. All in all, I'm sold for the time being.