The netburners are way too pricey.
Netburner SB70LC with 2 serial, Ethernet, and power: $100, assembled and ready to go.
Arduino with 1 serial, power, and Ethernet: $63, plus assembly and test time for the Arduino board. Plus time to write the Ethernet-to-serial app that's included with the Netburner in a form that's at least close to what you want.
I just went through this with my weather station project: going with the Arduino significantly increased the amount of time it took to get everything working. Much of that was due to the fact that the Ethernet shield is still relatively new, and doesn't have as large a base of re-usable code as the Netburner. Part of it was also due to the more limited CPU and memory resources on the Arduino. But the bottom line is that, if I had been charging all my time against the project, instead of writing off most of it as "investment in professional development", the Arduino would have been a bad choice.
Everybody has different priorities, and not all of them are purely economic. So I'm not suggesting that there would be anything wrong with your choosing the Arduino for your project. But I do think that your dismissal of the Netburner as "way too pricey" is overlooking costs that you haven't considered.
I also think that this shows we need an Arduino with an integrated Wiznet chip, which would dramatically lower the cost of projects with an Ethernet interface, but that's another thread ::)