One of these projects is the breadboard PSU. A slight change to the PCB foil layout frees up some additional space on the breadboard. I've just updated the download file for this project with an additional PCB foil.
Another project that I'm in the process of updating is my recent LED clock. I realised after construction that there were a couple of unused I/O pins on the PIC that could be very useful if they were brought out to one of the connectors. There were some other design improvements that became obvious once I started looking at other things I could do with the project.
Of course, a lot of these types of issues are because as hobbyists we don't peer review our designs. At work, all hardware and software projects are looked over by somebody else on the team; a form of sanity check, and it's amazing how a fresh pair of eyes can spot obvious omissions and mistakes.