Create a dedicated "CONCERT" page for all the bands that play in one night.
Instead of having one band's page link to another band that played that same concert (as it is right now, with the "related set lists"), or the main band having their supporting acts listed (as someone else suggested), there should be a main CONCERT page for every concert that lists all of the bands that played that night, their playing order, and maybe any other information related to the concert itself.
This could even lead the way to incorporating seating charts, and with that give users the ability to list where they sat.
As it is right now, it's very cumbersome to deal with an entire concert...having to find all of the different bands that played, adding them, and then having them show up as different concerts on your main list. With one MAIN concert page (that could feed into smaller, individual band pages for that show), it would make the setlist.fm experience a lot more solid!
Lasse David Sand Østergaard commented
Then again, many people will come just to see the support band and then leave, while others will show up just in time to see the headliner. Seeing them both IS seeing two concerts at the same venue.
Yes, I totally agree. I'm in the process of putting my total concert history on setlist.fm. And it is really annoying to have the count at a particular venue, twice as high, just because setlist.fm treats the support band and the headliner as two different concerts (also on the overall concerts one has visited). Also it really makes it overwhelming to look at ones concert list, when every concert is listed with an individual date, even though they belong together. That really is my biggest beef with setlist.fm at the moment.
I'm not sure this is the ideal solution to this, but I agree a solution is needed. Currently it says I've been to X concerts when of course I haven't because a great many were playing at the same show.