They took down a load of streets behind my street. They were on a map dated 1965 and were built in the late 1800s, but are now an industrial estate. If you look closely at Moorland Park you can see the crop lines of the old streets. Where's Tony Robinson when you need him?
I also discovered this evening (thanks to some detective work on 1901censusonline.com)that Moon Street in Splott was knocked down sometime in the late 50s/early 60s. Here's a picture of it on an old map:
And here's the view looking down Moon Street as it is now:
You can see the grass part curving over the hump where the old road and all the rubble is buried.