Good

I don't really care if people use FF, Opera, Safari, Konqueror or even Lynx; heck, even IE is OK, just so long as there is a good mix. Why?

1) It reinforces standards and reduces the potential for lock-in, leading to greater competition, increased quality and better value for money.

2) It forces software makers to ensure their product is more manageable. For example, FF is often criticised for not being easy to centrally manage, perhaps increased demand for this will get Mozilla to address it.

3) It encourages OS vendors to provide tools for managing same. Linux shows one way this can be done (one integrated system keeping the OS and all apps up-to-date automatically - something Windows users can only dream of).

4) It massively increases security. In a homogeneous environment a single-point failure can rip the entire system open as the exploit will work across all systems. In a heterogeneous environment it is much harder to get a full system break as you can only ever attack a certain sub-set at a time.

5) Sustainability. With a heterogeneous system it is also much more likely that some kind of service can be maintained, all be it reduced, should an attack or failure bring down one system type. In a homogeneous environment a single virus could bring the entire thing crashing down.

Although there are some costs involved (e.g. trickier initial set-up, training, extra staff) these can be offset by savings in other areas (e.g. reduced license costs, increase up-time, reduced maintenance).

I am not having a dig at MS (yet), *any* homogeneous system be it Apple, *nix or whatever is ill-advised for the reasons above. It is only hard to have a heterogeneous environment due to the deliberate actions of the current monopoly player, it's time customers struck back (there you go).