I operate a low-level iGate in Palo Alto, CA. It's built out of a WRT54G running aprs4r (Ruby) and using an Argent Data modem, based on an integrated design by Chris K6DBG.
I didn't hear the balloon directly, but I did hear it repeated from three mountain-top digipeaters (i.e., one radio hop away) and gatewayed the packet to the internet.
Here's the first packets I heard; the very first had a bad decode for most of it.
2011-12-09T17:13:02: K6RPT-13>APBL10,WR6ABD*,WIDE2:!????????/o?O???/???/A=109373
2011-12-09T17:15:06: K6RPT-13>APBL10,WR6ABD*,WIDE2,QAR,KG6HWF:!3715.25N/12153.29WO140/000/A=000193CNSP-13
2011-12-09T17:15:06: K6RPT-13>APBL10,WR6ABD*,WIDE2:!3715.25N/12153.29WO140/000/A=000193CNSP-13
APRS is based on AX.25 unproto, which is kind of the IP equivalent of UDP (as AX.25 is derived from X.25). It uses source routing, so you can see K6RPT-13 directed its packet at the "destination" APBL10, and the destination in APRS is usually a unique software identifier. That got picked up directly by WR6ABD on Loma Prieta mountain near Santa Cruz, CA. WR6ABD retransmitted it ("WIDE2" is a hope count for how to route over RF), and then gatewayed to the Internet ("QAR") by KG6HWF, and my WRT54G picked that up off the internet feed. The third line logs a packet I received directly and correcly from WR6ABD My WA5ZNU-10 iGate would have also done the same after the 3rd packet there.