Yes,but no. Once you get in the code of ac.scm, you see that the code is great (really easy to understand everything) but that it can really be optimized in trivial ways.
We already talked about arc<. The original code was : if all the elements are numbers, apply numeric + to the args. If all are strings, apply string-append. If all are lists, apply append. Else, apply numeric + (again). The optimization is obvious there, and I don't think it can be called premature.
There was another one that was fixed by pg in Arc2 (for those interested, it deals with ar-funcall).
I know I wasn't clear. I don't want Arc as fast as light right now. What really bugs be is the fact that I have to wait 3 seconds before I get the prompt. When arc.arc and libs.arc are loaded. That's what I would like to see optimized, as soon as possible.