(For links to web sites with "live" WXSIM forecast, click here).
There are (as of March 10, 2015) about 970 registered users of WXSIM. While in most cases I haven't inquired about their backgrounds, in casual exchanges I've found that most are simply amateur weather afficionados (many of whom have home weather stations), though there have been a number of educators, professional forecasters (both public and private), a couple of electric utilites, emergency management personnel, plus a couple of sailing or soaring (glider) enthusiasts and at least one ski slope operator. While the majority of these users (almost 500) are in North America, there are also over 400 in Europe and the Mediterranean area, plus scattered users in much of the rest of the world, including over 50 in Australia and New Zealand. The map below shows specific sites for which I've done customizations. The yellow dots represent jobs - 1100 of them - done mainly in the last several years (two of these are sample sites), while the red dots are older jobs (most of which are sample or practice customizations, but with several older jobs for customers as well). In some cases (such as at least half of the dots in Argentina, Finland, and Spain), multiple sites were done for the same customer. In other cases, multiple customers were geographically very close to each other, and the dots overlap.
Here is a close-up of North America, to better show the distribution of users there:
There is also a large concentration of users in western Europe, as shown here:
WXSIM works in the southern hemisphere as well as the northern, and there are quire a few users in Australia and New Zealand. Here's a close-up for of these countries: