...and for me, it just runs forever. Just tried it again with a 7750, then with a 6870 and even a Core 2 Duo E8400. What card and ATI driver version are you using? Leaving out the device-selection option causes it to exit with a list of available devices.
no ATI, a GTX580
does it spit out "Difficulty: *" or not?
It does.
I think I've figured out what's happening: oclvanitygen will only find keys wirh vanity addresses for non-Bitcoin address types. These commands work:
./oclvanitygen -D 0:0 -S 1
./oclvanitygen -D 0:0 -S -X 48 Lfoo
This doesn't:
./oclvanitygen -D 0:0 -S -X 48 L
The degenerate case where you just want an address appears to only work for Bitcoin.