Since an early disaster with the Pi's Linux filesystem I have been pretty careful about backing up any programming work over WIFI to my iMac. The last time I downloaded the full Linux image I also retained the file on the Mac. The one thing I had not done was to back the whole SD card. It turns out that my original stuff only took up about 2GB on my 16GB SD. But since then I have downloaded a lot of new software. This includes the the latest Linux updates, GPIO libraries, drivers for devices, and most recently, software to read weather reports as text from the Internet.
This AM when I booted the Pi up, my usual SSH (secure shell) from my iMac didn't work. Scary! Also, the activity light on my USB wifi dongle wasn't blinking. So I pulled the SD card out of the Pi, plugged it into a flash card hub on the Mac and immediately made a literal copy with the old UNIX DD command. I'm going to do that regularly from now on. Anyway, after I moved the wifi dongle to a different port on the USB hub everything worked again. So, no big deal. But now I'm fully insured against disaster.
I'm now waiting for some spring-clip connectors for breadboarding. Much less trouble than soldering pins on to flimsy wiring.