They are great, you will not find any other solid surface countertop that has more character and charm. Check out our website if you need some ideas. www.burcollc.com
I've seen some really nice ones. Don't think they yet have the cachet or resale value of granite, but they look really nice, and they can be customized really nicely into virtually any shape with built-in draining boards, etc.
Concrete has a very neat, versatile and very chic look - but it's not for everyone. Therefore the resale value, like Steve said, is not as positive as stone like granite. If you go with concrete make sure you use a professional as it is imperative that it is sealed properly. Concrete is more prone to staining and scratching than granite which is also why it hasn't found the universal appeal as those looking for low maintenance tend to shy away.
In defense of concrete, the scratch resistance of our countertops equals granite. Granite is less vulnerable to acidic stains, however, with the proper sealer you can pour red wine on a concrete countertop, leave it over night and not have any staining. Maybe longer, but no surface is completely stain proof or scratch proof. No matter what countertop you choose, you have to take care of it and not abuse it. As far as resale goes, i would have to do some research to answer that truthfully. I do know that the majority of concrete countertops are more expensive than granite. However, most people installing concrete countertops have no intentions of selling their home, they are customizing it to their taste.
The engineered-concrete we make is a little higher than a high-level granite top...but depending on what type of concrete you get, it can make a huge difference. Our line is Verdicrete: http://www.brookscustom.com/concrete-portfolio.php and I know it offers a lot more than traditional concrete (stain-proof, 30% lighter than stone, doesn't chip or crack, can mimic a lot of different materials).
Concrete is beautiful in my opinion and certainly more creative than the standard boring(everybody has it granite). I disagree that for resale you will suffer. I think people are over granite and I'm still concerned about the health issue with granite. Radiation exposure.