They both have macros, and ioke's syntax looks nicer to non-lispers than clojure's. Ioke (iirc) is considerably slower than clojure, and kinda difficult to optimize.
Throughout last year Ola mentioned many times in his blog, that he's not concerned with speed optimisation at this point, but mainly features. I'm not sure about the "hard to optimise" part... Also if you look at the Ioke manifesto[1]:
> This is really the full manifesto of Ioke, if you ever had to choose just one. In any situation where I have to choose between expressiveness or performance, expressiveness is always the answer.
Don't remember him mentioning anything about concurrency though.