I've had one in for two years now. It gave me three heads last year and it's re-shooting. Excellent.
My father in law reported that while he has about ten plants, he only got about five heads. So while he's away I decided I'd divide his plants and re-set his garden for great yields. When I go there later, I'll post some photos of his plot. But the upside is that I got some plants too.
They grow a woody root, and as long as you have a sprout of green, you have a new plant. And it'll give you at least one artichoke in the first year, by my experience. So I have a few in pots and now a line down the back of my vege garden.
Now all I need is to pile in some granular fertiliser, like rose food, and wellbe great.