Training? My dear old mom received some IT training for Windows 98 and Office back in the day -- she's gone on to use Kubuntu and Windows7 with Open Office without any additional training, not even "IT Support" from me. Office suites might change where they put things but people who use them tend to, in my experience, find where those things are as and when they need them. So, apart from the odd bit of confusion, I can't see much Office training being needed.
Then you have any browser-based forms and applications -- provided they'll work in Firefox or Chrome or whatever then it doesn't matter which OS the users of these are on because they never need to touch the OS. Same goes for anything terminal based -- will work through any old terminal client.
So, training going to Linux should be minimal fro a lot of organisations -- it's only those installing and configuring the software who need to know the differences. Anyone else should never touch the OS anyhow.
I'd say the only expensive barrier is replacing any proprietary or bespoke systems which rely on Windows -- in fact, that may make it cheaper to stay with Windows even under very expensive licenses.
There's an interesting, if old, article about Ernie Ball moving to Linux which seems to agree with my assessment also.