Which claims? That my productivity is improved? That I can run 12 to 20 applications simultaneously on an OS X Mac? That a Windows machine can start to significantly bog down with two or three?
Currently, I am posting this reply from a client's older OS X Mac Pro that doubles as his office server. It has four cores (2 x 2.66GHz Dual-Core Intel Xeons) and runs with 9GBs of 667 MHz DDR2 FB-DIMM RAM. There are four users currently logged on to this single computer and seven workstations connected to the database it is serving. All told, between the seven workstations, and the four users, I estimate there are about 40 active applications running with probably about 15 idling but all currently present in RAM... 12 on this user space alone. According to Activity Monitor, it is currently processing 140 processes with 559 threads. Included in those processes are four instances of Folding @ home that uses idle CPU time on the cores... No slowdown. UNIX is a strong, efficient OS.
None of the workers at the workstations can even tell that I am doing CPU intensive work on the server at all. One of the user spaces on this machine is accessing and printing the monthly statements... about 2000 individual print jobs... as I am posting. I don't notice it.
The server portion has sent 12.61 GBs of data and received 10.42 GBs of data since the database was started this morning... so it's been very busy.
Oh, incidentally, there is a OS X window with Parallels running WindowsXP Prefessional providing access to a Windows only database application that provides the workstations with data about patient insurance coverages...
You don't claim that it can bog down, but that it will. I have no patience for creativity when it comes to benchmarks and performance comparisons.