Twice...
My first experience in implementing ITIL was with a large (>35,000) publically traded corporation whose main focus was on SOX compliance - they figured deploying a many ITIL processes as possible using an integrated software solution (HP) would achieve this goal. Although we did well on the audit, what we achieved really missed the mark on whole point of ITIL, which is achieving a more business-focused/partnered IT organization - instead, delivering solutions to the business took longer, quality wasn't improved, and IT was perceived more as a disabler than an enabler.
Now I'm doing it again in a different organization, but this time without any SOX compliance constraints and with a much clearer understanding of how to do it right. Regardless of whether a business is regulated or not, I think ITIL provides an excellent framework. The most important thing to keep in mind is that it is a framework and not a religion and you've got to tailor it to meet the needs of your particular businss - what works in one company may or may not work for another.
