Just to keep everyone in the loop since I know there is SO much interest in my woes
Turns out that the firmware was a bit out of date (the firmware list I found on digi's website apparently needs some updating, too). Since updating (version 10CD for those keeping score), I've gone from a bad packet every second to none. So that's quite nice. Other notes from digi's support included setting the packetization timeout (RO) to 0x03. Probably decreasing the baud to 57.6k will ensure that I always get good packets.
One question, tho. Seems like it would be smart to implement some hardware flow control between the xbee and my arduino pro mini. I basically need the xbee to tell the mini to stop sending it data for a moment. This can be done on the xbee via the CTS pin (pin 12). From what I can tell, when the buffer is close to full the xbee sets the pin high. When things are OK, it sets the pin low. What I don't know is what to do on the mini side. Any advice? Can the CTS pin on the xbee be connected directly to one of the end pins on the mini? Or is this something I need to monitor in software on the mini? I'm a bit lost here.
Thanks in advance for any pointers.