I've always tried to enable gzip compression on web servers because it seemed to have very low CPU cost and you obtain a significant data transfer reduction.
Now I we have a public server that has not gzip enabled and sometimes it's CPU load is quite high under heavy traffic (mostly because complex SQL queries on certain pages) and reading this Microsoft article on the subject of enabling, CPU load should be taken in account when enabling gzip.
The client wants to reduce bandwidth and speedup page load times but I'm not sure that enabling gzip will do more harm than good, although it has worked well on other servers.
In your experience, will gzip compression have a significant impact on CPU load?
EDIT: In this case we are using IIS6