Hi daytrader.
Let me specify that I'm quite new to this world, so forgive me if say something really odd!
I've experienced the same problem as you posted:
ip 0.0.0.0
but I solved it by removing the SD card and reinserting it, then pushing the reset button.
A brief history.
I was using an old Arduino software (not sure which version) and all worked fine: happily connect to my arduino through Internet Browser.
Then I upgraded the software to 1.0.1.
Seems that some ethernet lib have changed.
The problem arises soon after (minutes) and I was no more able to gain access to my device through http 80.
If I ping the expected (encoded in the sketch) IP (192.168.1.177) I do have a response.
So there is some kind of communication between my router and the arduino device.
ARP -f show the mac id and the right IP.
Nevertheless the browser can't connect to the device and the serial monitor still show 0.0.0.0.
As I said...I just extracted and reinserted the SD card, and it start working again.
Not sure if this is the solution but it definitely have something to do with libraries and SD in my humble opinion.
Have Fun!
Gabriel