It took a while, and a few un-do's before it began to lay flat, but I got there in the end. If you make too many increases, your rug or circle will become wavy, and if you make too few, it will begin to form a basket.
I'm really very pleased with how it turned out. If I could do it again, I'd probably make it out of a tougher yarn, as it is really very soft and I usually don't even realise I'm standing on it!
This is the yarn I used, it's an 8 ply with variegated browns, grays and tans. I doubled it up with a black 8 ply acrylic and used a 5mm Size H hook.
All in all it didn't take long to make (if you don't count the un-do's and re-starts :/) and I'd love to make a bigger one in the future. Definitely cooler than just going out any buying one... and cheaper too :)