Does anybody record ambiences with a shotgun? I mean, it seems feasible if you are careful about it and then piecing them together in post. It almost seems more ideal since you can pick out the interesting parts of an environment for post.
Tim Prebble does. He's pretty good.
I do from time to time, depending on the source I want. For example, I got a really really marvelous crowd-sound from a big theater a while ago using an MKH 416! I got everything from cheering, applauds, laughter, and intermission talking. A cardioid here, as I was about four meters above ground, wouldn't have been much more that a diffuse murmur and sometimes near white noise, which I of course recorded too, with an Oktava 012 set and MKH 40's in different configurations, but with the shotgun you get a close focus with good details. The 416 is way too thin to stand by themselves though, and as all shotguns are a little too focused (which is exactly what I want) I would probably never use it all alone for ambiance at all, and that includes all shotguns, colored sides or not, as the soundscape often tends to be quite unruly and cluttered that way.
The 416 has a heavy coloration from the sides, and are anything but neutral, but I'm very fond of that and use it as a tool, both in effects and ambiance :-)
I've had good luck with my Neumann RSM191. It pulls sounds in closer than a cardioid setup would, so you have to be mindful about that, but that isn't always a bad thing. It's not my primary setup for ambience recording, but I'm usually happy with the results I get.
I recorded all of this rain with the 191:
Also this train station amb:
And this city traffic stuff: