ive just started working for an a/c company as a trainee installer ive been doing it for 6 months now and im picking it up pretty quick its like most things if you have a good trainer then its doesnt take aslong to pick it up. like ian's said splits are easy and it'll take a matter of months to learn how to install them but ive just moved on to vrv systems which is more complicated as your feeding to various units instead of just one indoor unit.
i'd deffinatly say theres a scope to travel round the world doing installs as all the best to go are hot so they all need a/c.