Having fun learning to use the DS18B20. It looks like it can take a while to read the temperature via the library. A second or more and the Arduino can't do anything else during this time. I guess the library calls delay().
I think I'll see if there is a way to read the data in a non-blocking manner. I think most of the time is just holding the line high to provide power in parasitic mode, other things could be done during that time.
I'd like to read the temperature fairly often, but still service 5 buttons.