Boot USB - No Network Connection

[Sim1]

Might be power issue.
I had similar issue when after vacation I booted 2 rpis, one with xbian and other running squeezeplug distro as music player and I switched psu accidentally. Xbian one uses dedicated raspberry psu and the music player is powered by normal Nokia phone charger.
Xbian started on Nokia but after moment lost connection and it happened every reboot, no way to make network work normally... then I realized I switched the power supplies and all was back perfect.
USB stick might take the amount of power to make ethernet work unstable.