We have a good few clients using Xero.
(we are Xero partners so resell, implement and train so I have a conflict of interest here)
There's at least a few hundred Irish companies using Xero at the moment.
Its relatively simple so lots of people get on with the package with very minimal training.
I've never seen a public training course.
In relation to cost it works out good value in comparison to paying support on a typical desktop product.
If you've any questions feel free to ask here and I'll do my best to reply,
Ralph