I'd be willing to bet over 90%. You can't do commercial and NOT use them. I like/prefer carriers and MGA's that allow online rating or data entry, but you just can't escape them entirely.
If all you do is personal lines, at the very least you ought to be using LPR/Acord 35, unless the agency you work for has developed their own form in-house for this purpose.
If agents write much commercial, they are deeply involved in ACORD forms. If they write mostly personal lines, the application / binding process tends to fill out the ACORD forms automatically, behind the scenes. The agent may print them and not even realize they are an ACORD form that they printed.
Personal lines usually have a carrier-formatted app. For the commercial lines, I don't know many carriers that don't use some kind of ACCORD form; maybe 80-90% use them. The number could be higher.