I've had my (non-trial) Dexcom since Thursday evening. The first sensor was crap, apparently. The trial one from the previous week had gone so well (after the first night, which was crazy), but this one seemed to give me numbers not even remotely related to the ones my meter showed me (Dexom 44, meter 126?! Dexcom 250, meter 160?! ), and it gave me ??? errors a couple times, plus a long and inexplicable out-of-range error... so after another insanely inaccurate reading followed immediately by ???, I finally ripped it off and started a new one Sunday afternoon.
I also wasn't especially pleased with the new sensor the first day and started wondering if it could be the transmitter or receiver... until that evening, when everything started going smoothly. And now, it's damn near perfect, staying well within the acceptable variations (20 points off on the low side, 20% off on the high side). Even over the first night (which gave me trouble on the trial sensor), it didn't throw me any usual numbers, and my fasting numbers matched pretty closely.
Ahhh, CGM bliss. I'm hoping Dexcom will replace that crazy sensor (I tried contacting them, but you know, it's Labor Day weekend). In any case, I'm once again so glad to have this tool. It's just too useful... when it works.