I wrote a little tutortial on how to get started with Ethernet here:
http://mbed.org/users/no2chem/notebook/ethernet-testing/

I included a testing application which uses DHCP and displays some status indicators and serial debug data. Personally, I think its a little better of a test app than the HexSniff and arp spam app because you only need a web browser to verify that your ethernet is indeed working.

I wonder if there is a way to make this stuff more accessible? For example, I found Rolf's page pretty useful, but I needed to do a bit of digging to find it...

I would agree..  Some method of making these things easier to find would be a great help to beginners.......like me..  I found this tutorial extremely helpful, as a few others and some very useful tips from others on this forum..  Although, I might have to ask less stupid questions if there was a nice index to browse rather than a search box that leaves it up to tags and the like to get lucky.  Call me crazy, and I've seen better.. but even parallax has a object browser for their propeller chip. 

At any rate, thanks Michael for creating the tutorial....and for posting this!

Michael, if you don't mind my asking...  How would one initiate a connection via a specific port to a specific IP address and send a small string to another device using this?

Nice, Very nice.