The latest word on the bitcoin transaction rate limit is that it's now reached 6 transactions a second. Wow! That certainly helps define the snail like transaction systems it might be used for, though the jury is still out on even that.
A recent article, rather catchily titled "Bittercoin: true blockchain believers vs. the trough of disillusionment", says:
"even if everyone in the world wanted to use Bitcoin — a very big if, given the irrevocability of such transactions — they couldn’t, because the Bitcoin network can only handle six transactions per second. The ongoing civil war is about the best way to deal with this restriction."