There was a question, some time back, about the cost of supporting full continuations with call/cc. Here's a very nice paper i found recently. Unfortunately, i have not found it on line: William D. Clinger, Anne H. Hartheimer, and Eric M. Ost, Implementation Srategies for first-class continuations, Higher-order and Symbolic Computation, Vol 12, number 1, 1999, p. 7-46.