I'm in the middle of developing a Scheme compiler for a future release of vCalc. While I've been developing the code, I've peppered it full of debugging print statements that look something like this:
(format #t "compiling ~l, tail?=~l, value?=~l" form tail? value?)
with the output statements in place, the compiler takes about 250-300ms to compile relatively small functions. Not great, particularly considering that there's no optimization being done at all. Anyway, on a hunch I removed the format statements, and execution time improved by a couple orders of magnitude to a millisecond or two per function. That's a lot closer to what I was hoping for at this stage of development.
On the other hand, I hadn't realized that my (ad hoc, slapped together in an hour) format function was running quite that slowly. I think it'll end up being an interesting optimnization problem sooner or later.