Nah- I'm just working on ph_storage and I've been trying to make sure all the glass in the place is breakable. For the inevitable spytech room, I've got a wall with two doors and half a dozen windows separating the actual spytech area from the 'front room,' akin to what you see in 2Fort. And while you can easily go through the doors to see that it is a spytech area, I got it in my head it might be interesting to have the windows as one-way mirrored glass that you could shoot out to reveal the area.
Granted, this is a prophunt map, so there's limited shooting (relatively speaking), but I still figured that it'd be a neat visual effect.
As for the questions about slick surfaces and ball pits, that was related to Team Interrobang's PropHunt map contest. One of the side prizes is for the map with the best slide. I was thinking a slick surface could help with that one (and the ball pit's fairly self-evident, I think). The fact there's another prize for the best environmental deathtrap means the alternative's just fine too.