Just try, in any large organization, to get the app owners to play inside the sandbox of upgrades.
-> RHEL4 still around because the development folks for a whole raft of applications "Cant get it to work" on RHEL5 or RHEL6 - what is it? apache proxy servers and weblogic.
(and for the record they *were* given sandboxed playgrounds with RHEL6 -- with 99% of the updating done - the WL app code apparently needs about a years worth of work before they can move it)
-> win2k3 32 bit - many many installations around - app teams own licenses for app code that will not *permit* them to move to another OS, or the app support folks just do not have the expertise to do the job.
environment is about 24k systems from 1U 2CPU boxes up and out to 128CPU Itanium systems and a couple of Z boxes (I believe we've just spun up a new box)
One month to move from one OS version to another just is NOT happening, never mind from one OS to a different OS.
In my department, we've got three left to move - one will be shut down and turned off - there's been a 7 month long effort to move to a new application set to cover that one. One will be forklifted over to 2k10 with a new version of the application code - this has been almost a 2 year effort since we had to start by uplifting the back end AIX based application, the database behind the application *and* all the data structures in 7 related databases on other platforms. The last one - we've moved 80% of the components to linux hosts (IIS to apache, msql to PostGreSql, and FTP (gag) to sftp) the rest is being migrated from an in house "document share" to SharePoint. The SharePoint migration is delayed for political reasons at this moment (Outsourcing by the way, sucks rocks in Sooooooooo many ways when it comes to changing course).
Yes, Microsoft is not always the correct solution, but then again neither is *nix always the correct solution - and in reality - linux is wonderful, its cheap and its far more common in business now, but the number of users for whom it is *easy* to move to linux is *small* relative portion of the population of end users.
I'm very much a linux shill - where its possible to get things on linux I will do so. However - it's not always the right thing to do, and it's not always possible.
the right tool for the job boys and girls, always the right tool for the job at hand.