we bought one on a whim a couple of weeks ago - the WV5 premium from the karaccher outlet store - £50 instead of £80, its ok, but as everyone has said, can smear, ive not used it on the car and probably wouldnt, the curves of the glass would be a struggle, but for the house windows... ive done them all and they are all better than before I did them! so i think it will cover its cost as opposed to paying someone to wash the glass.
all in, the best part is not the vac, but the squirty bottle with built in scrubby!