I don't believe this question can be answered.
I was actually surprised to find out just how few copies of "LabVIEW for Everyone" have been sold. Based on those numbers, and on my estimates stemming from numbers of programmers here in San Diego, and on attendance at NI, crossed with the serial number of the last version of LabVIEW I purchased, I have to guess that there are probably about half a million LabVIEW programmers in this country. However; there is no way to know.
You can find out how many copies of LabVIEW have been purchased, and assuming you only count versions 4, 5, and 6, come up with something of an accurate account. This won't be entirely accurate as it won't account for the many people who use unlicensed copies of LabVIEW (where I work
ed, only about a third of the copies of LabVIEW in use were licensed.) I also won't account for those who bought it, and promptly gave it up for, say, C++ or something else. It also won't account for those old-timers who still refuse to upgrade either their Macintosh SE, or copy of LabVIEW 2.x (I know of two of these...)
You can also find out how many people have active support accounts with NI. Of course, this wont tell you much either.
The number of participants here probably represents less than 25% of the actual programmers out there, and who knows how many of the Info-LabVIEW subscribers also use this forum, and how many use only one or the other (I don't use Info-LabVIEW.)
You can also just SWAG it. That's what I did, and it works for me. Of course, in writing a book, I am hoping that every LabVIEW programmer will want it, and I can sell more copies than "LabVIEW for Everyone", and make as much money as I do in a week contracting...
...speaking of which...that's
my two cents...