We have been trying to clean the clear glass windows in our house for years - tried every available cleaner to no avail - always had a milky look.
I had actually decided to change all the glass when my missus tried her "Danoz Direct" steam mop (yes, yes a TV special thigo) and I couldn't believe it - the windows sparkle so well you struggle to see there is even glass in the frames!
An amazing product and Gav is right - steam does the job, very well!