Client Level Programming
Client level programming refers to using a subset of a language to quickly get things done. It's possible to learn just enough VHDL to be able to tie cores together and make them work for you. Learning to use VHDL in this manner is much easier than learning how to define cores, modules, digital logic and all the things that go along with advanced VHDL programming.
Client level programming means that you are not going to be writing your own cores, which are like libraries in C. Rather, you will be just using VHDL in its simplest form to connect pre-existing cores together to derive the functionality that you need.
Cores
While the Arduino encapsulates advanced functionality in libraries the Papilio encapsulates advanced functionality in cores. Using cores in the Papilio is very much like designing a circuit board but instead of selecting chips one selects cores. Instead of drawing connections in a PCB CAD program one defines connections in Xilinx ISE using schematics, VHDL, or Verilog. Best of all, the design runs right away instead of waiting for parts and PCB's!