wvmarle:
Can you still blink the LED on any pin without the transistor?
Nope, I unsoldered it and all digital pins sit at around 1V, no blinking whatsoever. The builtin led is dark as well, it should be blinking.
What is surprising is that I can still upload sketches using Arduino as ISP (but not using Serial), so the pins still work for SPI.
I don't mind switching to a new board, but I'd like to understand what happened so as not to end up in the same place 
Franck