Don't forget though that, unlike running multiple instances of an .exe vfp process, the vfp mtdll shares the vfpt.dll runtime among all of its threads. This is very efficient for web apps. Each vfp exe process, on the other hand, runs with its own copy of the larger regular vfp runtime with all the associated overhead. This is fine for small web apps but watch out as you load increases.
It's been my experience that it definitely is not worth trying to share global memory among mtdll threads since it only shares memory among certain threads and is not "global" to the entire thread pool. If you really need to share data across threads, it's far easier to use the good ole dbf to do so.