Maybe because it's such a small leaved plant the word acre doesn't seem to apply? Approximately the amount of land tillable by one man behind an ox in one day. No, it won't cover an acre in one day.
This really is a great plant as it will grow just about anywhere, doesn't do well in very dry dense shade though. I find it interesting that it does well in any other light conditions combined with very dry. What an unusual, easy care plant. Another bonus, it will spread easily, but just as easily can be removed from areas you don't want it because it's roots are so shallow. What a great plant.

Chris, your first 'no idea at all' could be Sedum oreganum possibly? It's hard to tell the scale of it.

Jacki, if you click on the picture and enlarge it, it looks to me like the leaf pattern is different the oreganum. Oreganum looks like a rosette and the leaves on mine aren't. Mine is in quite a bit of shade though.....

The conditions certainly impact the growth habit. I don't know oreganum very well, I only just got one this spring, so I'm not totally familiar with it. See if it looks like yours...

Here is a link for more pictures of oreganum. Sedum (Sedum oreganum)
Here it is opening up into larger, flatter leaves.

Yours looks way smaller than mine, Lynn - the rosettes are about 1" across, but yours only look about half that.

I will take a closer-up (good English!) picture and post it to compare.....if it ever quits raining!

It's only because I was far away from the container when I took the picture Jacki. I will take a close up tomorrow with something for reference.