There are many ways to create a connection between multiple hosts. PLIP, like SLIP, allow a local connection between two machines, but uses the parallel ports.
Parallel ports transfer more than one bit at a time, this means it is possible to achieve higher speeds than with a serial interface.
The speed achieved depends completely on your hardware (CPU and parallel port) and system load, in general it may be from 5 Kb/sec up to even 40 Kb/sec.
The PLIP interface is fast enough to allow some decent tcp/ip functions, like NFS. So, you may have a computer with all your Linux stuff and another with only the minimal system, where you can mount all the rest from the main machine.
The disadvantage is that most users have only one parallel port, this means that you won't be able to print and use PLIP together. Even with two parallel ports it is impossible to print and use PLIP without using kernel modules.
This disvantage can be also eliminated, if you have two or more parallel ports, applying a patch that you can find in this Mini-HOWTO.
Finally I am now able to give a hopefully good way to set up a PLIP link between DOS and Linux.
I won't stress it enough: so far nobody reported a successful link between Linux and Windows95.