My neighbors DIY their countertops with concrete. The husband is a cabinetmaker so he is handy. They had a bunch of friends come over to help them. They didn't seem to think it was all that big a deal. As an outsider, I can say that their kitchen does look beautiful. It has a fairly modern look. The counters are slightly rustic. You might need to practice a bit before trying a whole countertop.

Here is a blog entry from an occasional GWer who carefully wrote his project up on another site.

Here is a link that might be useful: Concrete countertop blog

The short answer is that it is a ton of work. So if you like crazy DIY projects and you are a little OCD, then you might really like it.

I've done five and assisted on two others. I invested about $500 in tools (angle grinder with a wet polisher, vibrator, pads, etc). I started with a small one in the bathroom. That is a good way to understand the properties of concrete. But, there are challenges when you get bigger. For our L kitchen, I had to build a level platform in the backyard where I could pour and polish it. I think I spent about 60 hours on that counter all said and done...