Who in your house cleans the windows or do you get someone to come in? What about inside and outside windows?
I clean our own windows when I remember as we used to use a local company who used just water, but they got very expensive very quickly, and I swear they didn't attend half the time
(I used to work full time, now a SAHM)
How often your windows get a clean? (inside and out)?
I haven't cleaned them in years months! The outside was cleaned, maybe a year or so ago?? The inside, even longer! 
I blame DH, as I had a lovely little window washing kit from Lidl I think, which had a little sponge and a squeegee, and a box to keep it all in (which I used for the soapy water). And the git shoved it in the shed in one of his cleaning-the-house frenzies, and I've never seen it since
How much time would you/ your partner be prepared to spend cleaning the windows in your house? What problems, if any, are encountered?
I would probably spend about an hour cleaning my windows.
My house is a bit of a challenge, as it's a coach-house, so all my windows are on the first floor. This is a doddle for the inside, but the outside is a little trickier. We have windows which, thankfully, you can adjust so that you can clean the outside from inside the house.
Had you heard of the Kärcher Window Vac before today? Do you have one in your household? Would you contemplate trying one out? Why? What do you think of it? Where else do you think you'd use it?
I have heard of the Kärcher Window Vac - I wish I had one!! I would love to try one out, as I admire Kärcher products greatly, but just can't afford them.
I think the window vac is a brilliant idea, especially for houses/flats like mine. And so versatile - I'd like to try it out on the cars, especially the inside of the main windscreen. (can it be used upside-down??)