This port number is widely used on the net for MUDs (Multi-User-Dungeons), a type of chat system. It is also frequently used as an example port in code demonstrations or as an alternate HTTP port. The reason this is so popular is becuase it repeats the number 42, a popular number among computer geeks. In Douglas Adams classic book "Hitch Hikers Guide to the Galaxy", the number "42" is the answer to life, the universe, and everything.
This port is used (TCP) for a remote admin Trojan called "Virtual Hacking Machine".
This port is used for configuration for the Payline e-commerce package.
Connectix VideoPhone uses this port for something.
IBM's version of UNIX, AIX, has a C++ source browser (part of IBM's CSet package) that listens at this port and is susceptable to a buffer overflow.