Ok, I got some of this ordered (£4.99 + p&p) to try out:
Supposedly lasts a month or so between coats so time will tell. Developed by the same person who patented RainX (which apparently you can make yourself if you do some Google-ing!), it is said to fill the tiny pores (with special nano stuff!) in the glass rather than just put a water repellent coating over the top of the glass.
Went on very very easily - one coat, then second coat, polish off.
I used the 'nano' cloth it came with to apply it, then a (courtesy of GeordieBandit!) microfibre cloth to polish it off - absolute doddle to apply, shined up very well with none of the haze that RainX seems to leave until it's gotten wet. Certainly prefer applying this to RainX. Hardly needed any of the tube for each coat, it spreads very easily.
No rain yet, but I'll report back once it has!