I have an estimate, but only for the customers that I serve and I am unwilling or unable to supply documentation of this.
About 25% are currently using OPC only. About 65% use it sometimes.
On a side note, I found it annoying that all the apostrophes and quotations were replaced with &rsquo (and the other HMTL codes for them). Maybe it's just my browser not rendering something correctly? But both newest IE and Firefox don't display them correctly.