Looking at the boot sequence:
  Begin: Running /[   40.126206] EXT4-fs (dm-1): mounted filesystem with ordered data mode. Opts: (null)
  scripts/local-bottom ... done.
  done.
  Begin: Running /scripts/init-bottom ... done.
  [about 1 minute delay]
  fsck from util-linux 2.19.1
  fsck from util-linux 2.19.1
  /dev/mapper/trunks-lv_root: clean, 356330/1954064 files, 2538052/7812096 blocks
  /dev/sdb1 has been mounted 27 times without being checked, check forced.
  /dev/sdb1: 237/62248 files (0.8% non-contiguous), 73465/248832 blocks
    * Starting configure network device security                            [ OK ]
    * Starting configure network device                                     [ OK ]
  ...
  Ubuntu 11.10 trunks ttyS0

  trunks login:

When I log in:
  # brctl show
  bridge name     bridge id               STP enabled     interfaces
  br0             8000.000000000000       no
  virbr0          8000.000000000000       yes

I don't see any noticeable errors on boot. I see a few of the following entries:
   * Starting configure network device                                     [ OK ]

I sometimes also see:
  Waiting for network configuration...
  Waiting up to 60 more seconds for network configuration...

Looking at kern.log, I see:
  Dec  2 02:50:52 trunks kernel: [   45.113211] device bond0 entered promiscuous mode
  Dec  2 02:50:52 trunks kernel: [   45.113221] device bond0 left promiscuous mode
  Dec  2 02:50:52 trunks kernel: [   45.113224] device bond0 entered promiscuous m ode
  Dec  2 02:50:52 trunks kernel: [   45.113226] device bond0 left promiscuous mode
  Dec  2 02:50:52 trunks kernel: [   45.115598] ADDRCONF(NETDEV_UP): br0: link is not ready
  ...
  Dec  2 02:50:52 trunks kernel: [   45.235355] FS-Cache: Loaded
  Dec  2 02:50:52 trunks kernel: [   45.258321] FS-Cache: Netfs 'nfs' registered for caching
  Dec  2 02:50:52 trunks kernel: [   45.378114] bonding: bond0: Setting MII monitoring interval to 100.
  Dec  2 02:50:52 trunks kernel: [   45.378143] bonding: bond0: Setting up delay to 200.
  Dec  2 02:50:52 trunks kernel: [   45.379966] bonding: bond0: setting mode to 802.3ad (4).
  Dec  2 02:50:52 trunks kernel: [   45.380734] bonding: bond0: Setting LACP rate to slow (0).
  Dec  2 02:50:52 trunks kernel: [   45.382597] ADDRCONF(NETDEV_UP): bond0: link is not ready
  Dec  2 02:50:52 trunks kernel: [   45.408253] bonding: bond0: Adding slave eth3.
  Dec  2 02:50:52 trunks kernel: [   45.490835] bonding: bond0: enslaving eth3 as a backup interface with a down link.
  Dec  2 02:50:52 trunks kernel: [   45.491929] bonding: bond0: Adding slave eth2.
  Dec  2 02:50:52 trunks kernel: [   45.493123] init: udev-fallback-graphics main process (1634) terminated with status 1
  Dec  2 02:50:52 trunks kernel: [   45.574310] bonding: bond0: enslaving eth2 as a backup interface with a down link.
  Dec  2 02:50:54 trunks kernel: [   47.293867] igb: eth1 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX
  Dec  2 02:50:54 trunks kernel: [   47.294899] ADDRCONF(NETDEV_CHANGE): eth1: link becomes ready
  Dec  2 02:50:55 trunks kernel: [   47.944385] igb: eth3 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX
  Dec  2 02:50:55 trunks kernel: [   47.987913] bonding: bond0: link status up for interface eth3, enabling it in 0 ms.
  Dec  2 02:50:55 trunks kernel: [   47.987917] bonding: bond0: link status definitely up for interface eth3, 1000 Mbps full duplex.
  Dec  2 02:50:55 trunks kernel: [   47.988804] ADDRCONF(NETDEV_CHANGE): bond0: link becomes ready
  ...
  Dec  2 02:50:55 trunks kernel: [   48.571065] igb: eth2 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX
  Dec  2 02:50:55 trunks kernel: [   48.586656] bonding: bond0: link status up for interface eth2, enabling it in 200 ms.
  Dec  2 02:50:55 trunks kernel: [   48.786228] bonding: bond0: link status definitely up for interface eth2, 1000 Mbps full duplex.
  ...
  Dec  2 02:51:56 trunks kernel: [  108.607424] ADDRCONF(NETDEV_UP): virbr0: link is not ready

I am attaching a copy of kern.log