I have made a few projects with the pro mini. The problem is that it is not very reliable. My last project includes a digital pot with the signal line beefed up to 5V (from a 3.3V board), xbee and an optocoupler. From what I can see, the sketch works fine, but the 0-5V sweep output from the digital pot varies a lot. Am I drawing more current than the pro mini can handle? I haven’t tested yet with another power supply, but my last project worked only after I made a custom board.