We considered a few different options for our countertops—marble, black granite, and various recycled compounds, but, ultimately, we settled on wood. They were an economical choice, and we thought they'd bring a warmth to all the white surfaces. We chose the Numerär countertops from Ikea in oak. They come pre-sanded and with a light coating of oil, but otherwise untreated against wear and staining.
Part of what appealled to me about the wood was that it would age, develop a patina and show some wear and patterns of use, but, at the same time, I wanted to protect it from moisture and decay. I looked around for a finish that was food-safe and not volatile. I settled on spoon-oil—a mixture of beeswax and mineral oil used to finish wooden spoons and bowls. I wasn't thrilled about using petroleum-based mineral oil, but it was inexpensive and is safe to ingest (it's sold as a laxative).
You can read about how I made the spoon oil (and other uses for it) over at 3191 Miles Apart. To treat the countertops I gave them a thorough sanding with fine-grit paper and just rubbed in a thick coat of the spoon oil. I left it on the wood a good 24 hours and then wiped the excess and buffed them smooth. I was really pleased with the subtle boost it gave to the wood and the smooth feel, but they are still somewhat susceptible to staining and marks. I am working it into my household routine to quickly sand out any discolorations and apply more spoon oil about once a month. This really doesn't feel like a hardship to me, but the upkeep is something to consider when choosing a natural oil finish.