I had a problem with NICs and udev.
I tried to get in touch with Patrick Volkerding, but no reply..

Reproducing the problem:

Well, I did the tests with 2 setups. One of them:
00:14.0 Bridge: nVidia Corporation MCP51 Ethernet Controller (rev a3)
04:08.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8169 Gigabit Ethernet (rev 10)
Plus a USB NIC. When I booted with the USB NIC plugged in, 70-persistent-net.rules went...
Then, for testing, restored the file, took out one NIC.
Then, without the USB NIC, 70-persistent-net.rules had only one NIC, and always round robbin after each boot.

Suggestion for a patch: (on 2009-04-14, against current as of 200812010258) rc.udev.patch