95% of my miles are on my two utility/commuter bikes. Those both have 8 speed drivetrains, with friction shift, and I get 3-4 thousand miles per chain (I go by the Sheldon Brown method, measuring with a ruler, although I also have the park chain checker tool). I use the SRAM 8 speed chains, which are relatively inexpensive and easy to put on. Clusters last a relatively long time, but if I get lazy and don't change a chain and wear out the cluster, it is no big deal since they are not too expensive and with friction shifting, I am not so sensitive to having everything in perfect condition.

The other 5% of my miles are on a 'fast' bike which has a campy 10 speed drivetrain. I use campy chains on that, and replace them much more frequently - largely because the campy 10 speed clusters are so expensive. When everything is tuned right on that bike it is a sweet ride, but it is definitely much higher maintenence.