Any professional application that I've used or plan to use requires a strong floating-point unit; it's little wonder an Athlon 600 was about twice faster than my P3/450 in several of them.
Extra flavors like MMX can speed up simple tasks that are easily parallelized. Videocard analogy: your videocard accelerates simple, strictly limited pixel operations very well; but for any expandable image processing, you're stuck with software mode, whose versatility is unmatched. Likewise, parallel MMX only suffices for basic tasks, perhaps doing software T&L (which videocards are taking over anyway); for any versatile application, you're back to your FPU.
Intel's inclusion of their MMX2 playtoys is no excuse for their unacceptably weak FPU. If it's as weak as Tom suggests, I entirely agree with his conclusion--it's more of a fashion fad than a workstation chip.