Steam's support on OS X is the suck. I don't know what the experience is like on Linux, but given there is less competition from better stores on Linux I wouldn't be surprised to see Steam be a big hit on Linux.
As for me, after being a steam user for years, but given the fact that I haven't been able to play team fortress for 5 months now despite playing it for years, in the future, I'll use the Mac App Store.
As for me, after being a steam user for years, but given the fact that I haven't been able to play team fortress for 5 months now despite playing it for years, in the future, I'll use the Mac App Store.