Another good example of inheritance used in "real life" is the Bioperl open source project. There is, for instance, a Bio::Seq object, which encodes a general sequence. A variety of other types of sequence inherit off this general one.

That project also makes use of a lot of interface and factory classes (which I've never really understood well, so anyone who can explain will earn my ever-lasting gratitude). For example, a current discussion in the project is the development of wrapper code for the BLAST series of software programs. One idea is to generate a BLASTI (I = interface) class, along with accessory codes for all the others. In that way, anyone using a BLAST tool has a core standard interface to use & learn.