As of Jan 2019, Uber is available throughout Costa Rica, but is hit or miss outside of San Jose. There are pending government / legal actions that could impact the service in the future, but for now, it is available.
Taking Uber from our semi-steep, rocky, winding, dirt road to a town about 15 minutes away costs about 2900 colones ($4.80 USD). The same trip via an official red taxi is about 4800 colones ($7.94 USD).
1. If you are outside of San Jose (or bigger towns): when an Uber driver accepts your ride request and they are more than 5-10 minutes away, you may want to offer them extra money in the chat window so that they will actually pick you up. A little extra incentive goes a long way, no need to tell them how much; just knowing they will earn more is sufficient. We have had countless drivers accept, make you wait five or ten minutes, then cancel.
2. If you are lucky enough to find a driver you are comfortable with, offer to pay them cash to wait while you shop and take you home afterwards. Many are happy to do so. Also, get their phone number to WhatsApp or call them for future trips. We have found most drivers are eager to give you their contact information when you pay well enough.
3. If you have more than four people, you are out of luck. Uber may tease you with the UberXL button, but no, it isn't available. How about UberPlus? Nope, not available either. Consider a Taxi van or private transportation, but expect to pay much more.
4. Children under 12 are required by law to sit in booster seats. Yes, you read that correctly, Costa Rican car seat laws are stricter than those in the US. With a few exceptions, your Uber driver won't have a car seat or booster seat and Uber doesn't allow you to request it like you can in the US. Occasionally, the police setup checkpoints, even in rural areas, stopping each car to check registration, insurance, and any other violations. Don't be surprised if your driver does a quick u-turn when they see a checkpoint and your ride is delayed.
5. Dirt roads are part of rural life in Costa Rica. Most drivers will attempt them, even if they are rocky and challenging. Don't be afraid to ask.
P.S. get the phone number for the local taxi company for the inevitable, heart wrenching moment that Uber fails you.