I have the same problem. My eth0 fails at boot and it won't work even if I create a new connection. I have a LAN-connection to SDSL with HomePNA-card and I use DHCP.
Still I can see data running through eth0 when I monitor my connections. But I can't get to Internet.
This is what dmesg says:
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pcnet32.c:v1.27b 01.10.2002
tsbogend@alpha.franken.de
pcnet32: PCnet/Home 79C978 at 0xd800, 00 30 be 00 2a 24 assigned IRQ 19.
eth0: registered as PCnet/Home 79C978
pcnet32: 1 cards_found.
8139too Fast Ethernet driver 0.9.27
eth1: RealTek RTL8139 at 0xe1944800, 00:10:a7:16:b3:4c, IRQ 17
eth1: Identified 8139 chip type 'RTL-8100B/8139D'
NET: Registered protocol family 17
mtrr: 0xe0000000,0x8000000 overlaps existing 0xe0000000,0x1000000
atkbd.c: Unknown key released (translated set 2, code 0x7a on isa0060/serio0).
atkbd.c: This is an XFree86 bug. It shouldn't access hardware directly.
NET: Registered protocol family 10
Disabled Privacy Extensions on device c035fa20(lo)
IPv6 over IPv4 tunneling driver
cdrom: This disc doesn't have any tracks I recognize!
cdrom: This disc doesn't have any tracks I recognize!
eth0: no IPv6 routers present
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...probably something wrong with IPv6, but what?