Gal, I wonder if yours is faulty in some way? I get no lines or smears whatsoever. My parents have one too and they're really fussy about clean sparkly windows (I always remember windows being cleaned inside weekly, and weather depending the ground floor outside too - please tell me that's OTT?) so borrowed mine before buying to see if it passed their test, they get a lot of condensation in Winter so were wiping down windows daily which took ages. They loved it so bought their own.
I use it for the shower screen too, mirror doors on wardrobes and the bathroom and kitchen wall tiles. All come up shiny and streak free!
Frank, I think the idea behind meths in the salon was that it'd cut through the layer of hairspray that settled on the mirrors. My last job of the day, I hated it. I'd see that purple liquid and start grrrr'ing