I called Apple Tech Support and went through 3 people before they escalated me to engineering. They send me their data collection script to run. It uploaded about 366megs of data to Apple, so I'm hoping they will be able to tell me why it's doing what it's doing.
For more background, I have 4 VLANs. One for internet (xxx.xxx.xxx.xxx), one for LAN (10.0.1.x), one for Guest (10.0.2.x), and one for configuring the switch (192.168.x.x). Everything worked in SL. In Lion, when I turn on the NAT service, it wants reassign the IP addresses of all of my interfaces. So they all end up with IP addresses in the 192.168.x.x range. Obviously this hoses up all the configs. It's like it's deciding to run the gateway assistant for you.
So that's my problem. Hopefully Apple gets it sorted w/o having to wait for 7.1. For now I've had to rip up my network config and use an airport extreme with the wireless turned off as a makeshift router. Unfortunately the airport doesn't support VLANs so half of my network is in the dark.