A few weeks ago, the landlord had the windows in my flat replaced. It's had some interesting effects.
The most obvious effect is that there is almost no condensation on the windows. Previously, there was so much that the flat almost seemed to flood. Today, with all the snow outside, there was a very small bit around the bottom of one window.
More interesting is the way the flat feels bigger / brighter. The windows are white, rather than the previous brown, and with the double glassing, I'm not keeping the curtains closed to keep the heat in. This makes the place so much brighter, and I think this is making me more awake / energetic. I do appear to be getting a bit more stuff done.