Actually, it's more likely to be the other way around: the thing that's going to slow down the most is system calls. If the program is doing a lot of number crunching, it won't slow down. If it spends most of its time waiting on slow input devices like the keyboard and mouse, the slowdown probably won't be noticeable (I haven't noticed any slowdown). Programs that do a lot of disk or network access, especially databases, will suffer the most. And even that will probably be handled by scaling the back end -- any retail business that can handle Black Friday will add one or two more servers and you'll never notice.