Oh, good post Tosh.........
Mmm, skilled or semi skilled (unskilled doesn't come into it)......
As far as window cleaning itself goes I would say semi skilled without a doubt, within 3 to 6 months you can be an accomplished window cleaner, though in fairness it takes a few years before you become a 'seasoned' window cleaner.
We are always learning aren't we? But I would say it takes several months at least before you become that 'average' window cleaner I'm always banging on about

As a decorator I'm 'skilled' I served an apprenticeship of 5 years, and looking at the decorators that are unnder 30 years old it makes me weep (well, almost) for the lack of ability and skill that is being displayed.
Compare the two trades (window cleaning and decorating) most think its easy to clean windows, ditto decorating, whats hard about dipping a paintbrush in a pot of paint and daubing it on a bit of skirting or painting a wall...childs pay.
Without going into it in detail, decorating is a highly skilled job that takes years to master, and there are many complex issues involved.
With our trade it is much more straight forward.
It is skilled, but I would class it as
semi skilled. you watch a seasoned window cleaner in action and it looks so effortless, he will make it look so easy that anyone would think they can do it, but it takes a couple of years to reach that level....
Mmm, lets think....Newbie>>>>Novice>>>>>Acolyte>>>>disciple>>>>>master!
Well after 22 and a half years I think I'm a master! (but I'm still learning grasshopper!)
............its still semi skilled though
Ian