My above ground pool is 12 years old, so I have some experience here.
As others have said, the wet side is very durable. The impeller and pump housing will last forever, so long as the strainers are removing the big chunks of debris, and you don't let it freeze with water in it. The seal on the ceramic impeller bearing will start to leak after several years, but it is cheap and easy to replace. Go ahead and replace the ceramic bearing at the same time.
Far and away the weakest link is the front bearing in the motor. If you leave the pump outdoors over the winter, it will fail about every four years. While the bearing is cheap and straightforward to replace, it is not easy (at least on my pump motor). Bring the pump indoors for the winter and it will last a long time.
Pump motor switches also fail fairly often. The in-rush current and inductive load nature of the motor just eats mechanical contacts up. Nothing you can do about this really.
Other failures I've had (and fixed):
1. The foam gasket on the moving plate in the multi-valve came loose from the plate and tore. The whole plate assembly can be replaced for not too much money.
2. The shaft on the multi-valve plate snapped. Again, the whole plate assembly isn't terribly expensive. You do need a big vise or c-clamps to hold the valve unit together (strong spring!) while re-assembling.
3. The crappy hoses that came with the pool failed after about 4 years. I use some sort of hoses from Rural King (a farm supply store) that has hard spiral plastic on the outside. It lasts forever.