It's always been kind of painful, and I wonder is a good tool for the job. If planned ahead of time, putting an enclose on a mill and doing everything at once works great, assuming the enclosure will fit. For round holes step drills and knockout punches work well. Hole saws sort of work, but not very well. For rectangular holes I used to use a dremel with a saw wheel or and angle grinder. Trouble is that the dust level is pretty bad. No big deal if you make the enclosure first, clean it and then put stuff in it, but can be a real pain if you have to add holes to an already finished or near finished enclosure. Have any of you guys came across a tool that makes this easy? Some kind of nibbler perhaps?