One of the things we wanted in our new farmhouse was concrete floors. We loved the idea of being able to really clean them and we also like the price. What we didn't want was the dark stained look. What we have is natural colored sealed concrete. It is mostly gray but has some brownish tones from some very watered down stain that I sprayed on it. Honestly, most of the brown came from dirt during construction. It's not perfect but we feel that the hairline cracks, pits, stains, and worn areas give it a casual, well worn, comfortable look. It is not polished but you wouldn't know it to see the light reflect off of it during the day. It looks contemporary too.
This was one thing we did ourselves. After framing, we hosed it off and sealed it with a water based concrete clear sealer from Home Depot. Spraying it on with a pump sprayer was a cinch. Aftere it dried, we covered it with heavy brown paper and miles of masking tape. When the sheetrocking was done, we took that up. Finished floors! We did have to remind other contractors not to write on it.
Because we have 3 boys and 2 big dogs, we vacuum nearly everyday. To really clean them, we mop once every 2 weeks. After construction was done, we mopped on a wax which we will reapply every year. Basically, sealed concrete floors couldn't be easier. They are a great fit for us and our farmhouse.