I thought good beer got nasty after a few months and the yeast started clumping
big, dark beers such as imperial stouts and barley wines usually get smoother/better with age. Highly hop flavored and aroma'd beers such as imperial IPA do not get better with age.
Most of the time there is little to no yeast remaining in a production brew, but even if there is some, it will drop to the bottom and become sediment (dregs) that you avoid stirring up and avoid drinking. If there is too much yeast remaining and the yeast cell is compromised, it can impart a bad flavor to the beer.
- Torg