AVR-Chat

>For best EMI performance, when the ground is laid in 
>by hand you need to form a grid, not just a meandering wire, with 
>apertures in the grid as small as possible. This provides multiple 
>return paths for signals and greatly reduces emission of and 
>succeptibility to EM interference. Of course, if things are really 
>bad you need a full ground plane but at minimum you need a grid.

Well.. I have a lot of success with the anti-grid approach, providing one and ONLY one low impedance path back to the source, and not allowing RF current to spread out and take all possible paths.