Bad run of flatting on commutes continues. This time I made it all the way into work before the slow leak reached a flat stage. Took the tire and (front) wheel over to PB at lunchtime to see if there was something I was missing, other than a defective batch of Forte tubes (third one in my last three commutes). The mechanic couldn't find anything in the wheel or tire that could be causing the slow leak to happen (pin size hole again), chalked it up to another defective tube (ugh!!!). Replaced it free of charge with a new conti tube, so we'll see if that works out better. Now I just have to deal with the rain on the way home, but (knock on wood) hopefully no flats.