Beware the way locals drive: racing along the narrow and bendy roads in the hills. Many companies offering car hire ex.: Avis or Only Sardinia Autonoleggio.
Olbia has the only mall and only McDonalds for hundreds of miles. To most, that is a good thing.
Ristorante Gallura is certainly one of the best restaurants in Italy; it may also rank among the great restaurants of the world. Rita Denza, the chef, has been there since 1945, and she has an absolute mastery of the kitchen.
You may encounter poor road conditions, with potholes and open grids. Also the skill of some drivers leaves something to be desired. For girls it's better not to walk alone late at night, just to avoid the possibility to meet drunk homeless (usually harmless though).