We have not used a set list in about 14 years. I have been in my current band (yep) for 14 years. We have a master song list. When a song is starting to get to an area of transition, the next person who will be singing must choose a song or someone will choose it for them. The songs never stop. There is always some sort of jam/transition music between songs. Key changes and such are all part of that. For full beat/groove changes, the drummers (we have 2) will do some sort of cymbal wash fade kind of thing and the guitarists (we have 3) will start out the next tune. It is my job to fill in the gaps with the guitarists and drummers. Everything is done on the fly and to the audience reaction. If we are playing a certain type of tune that is really going well, we stick with another similar type tune, if the tune is a bomb, then we change it up. Worked for us for 14 years and counting.