Eventually one of the customer did hit a process virtual address space (AKA “Virtual Bytes” in performance monitor snap-in, a counter under particular process) limit (yeah, we are talking about 32-bits here) putting enormous amount of hardware onto single server machine. They seems to be satisfied with performance still (quote unexpectedly, they really attached a lot and they had to use several Gigabit LAN adapters to cope with the traffic!), the only point of concern is that everything sometimes goes into “out of memory” problem for no apparent reason. Thus 64 bits are already becoming really required (yes, we need to consider adequateness of our memory consumption too).
RAM, Virtual Memory, Pagefile and all that stuff is a nice introduction into memory terms.