How feasible is it to edge plate a PCB or at least a portion of one? I've seen it done but as I understand the outer edge is only cut after plating at most fab houses. Is this something that's commonly possible? I'm currently working on a board that would benefit from this as it slides into a metallic case and needs to be connected to it.
If you mean solid edge plating (rather than castellations) then it's certainly possible, but you will have to ask your PCB house if they can do it. As far as I am aware it's not too hard to do, it's just not such a common requirement (good for EMC behaviour).
One of the few prototyping companies that offers this option regularly is PCBWay.
It's quite feasible, and also known as Castellations (because they look like the turrets of a castle). It's used on solderable modules like these Telit GSM modules.
A detailed view of castellations:
Some prototype PCB shops will do it for you. If you're in Europe, try Euro Circuits or Hi-Tech Corp. In America try Saturn Electronics. But talk to them first about pricing, and how you define them in your Gerber data.
The board on the radio product that I work on has its edges plated so that it makes contact with the metallised housing and screens. The most important thing to ensure is that your internal power planes do not come to the edge of the board and short to the edge plating.
During the manufacture the edges to be plated are cut by milling slots in the board material. I believe that these edges can then be plated at the same time as any plated through holes.
Edge plating is no big deal its simply a matter of routing the slots at the same time as drilling the via holes prior to electroless copper plating. The image is then formed with photo resist and the electroless copper is re enforced by electroplating copper then either tin lead or gold as an etch resist. Obviously make sure any inner layers are not shorted out by leaving a gap before the edge plating. In Europe try Telydyne Labtech in the UK, or Optiprint in Switzerland.