This is quite interesting, I work for a _big_ oracle and unix shop and we've recently being discussing a new standards document which says that in future we'll be running the following:
x86_64 Windows (virtualised, if poss)
x86_64 Linux (virtualised, if poss)
We questioned replacing RISC/Itanium/Sparc with x86 and the cost makes it a no-brainer. The cost difference between similar PPC and Intel cores is something like 10k per core.
We then questioned running linux on Z and again, the cost was far less than we expected. NB: It was pointed out that if we weren't an existing (very big) Z server shop it wouldn't work, but the extra cost of running zlinux was piddling because of this.
My only concern is that linux is not as mature as existing 'big three' unix, but considering the cost difference and that we can use 'big unix' as an exception to policy if it's really needed, I can't say that I disagree... Much as I thought I did when I initially heard about it.
Anon for reasons of not discussing details of a big company's IT strategy in public...