It is good to see mainframes getting some positive press again. I'm talking about this November 17, 2005 article published in InfoWorld. It talks about a company that tried to get rid of its mainframe and replace it with first, Windows servers; and when that didn't work, Unix servers. When neither worked for them, they finally gave in and moved back to the reliable environment provided by mainframe computing.
Basically, it boils down to this. There are some workloads that just are better off being served by mainframes. This is the parallel I like to draw:
If you are going to plow a field, what animal(s) would you choose to drive your plow: a nice strong, sturdy ox (mainframe) -or- 64 chickens (Unix servers) -or- 128 gerbils (Windows servers)?