We had a very brief stop in Uyuni. We had planned to stay over for a night but the buses the following day were fully booked so we booked tickets for that evening and spent a short 6 hours there. The town itself was very small and its main purpose is as a starting and finishing point for the tours so we weren't too disappointed, we just weren’t looking forward to a 12 hour bus ride.
We walked around the town, spent some time in the internet café booking a hostel for La Paz (which took ages with the slow internet) and sat in the main plaza enjoying the sun with a bunch of people who we had met on the tour. It turned out that most people were heading out of Uyuni that night as well so we all went for dinner together before catching our night buses.