Hello.
I'm working on a project with a webserver and the ethernet shield based on W5100. As many others reported my Arduino stopped working after some access to the webserver. Now I'm sure this comes from the example which is provided with the ethernet library. As you can see there are lots of lines like client.print("something"); There must be a bug in the library or ethernet controller. Because this causes the hangs after some accesses! Now I store all my html code in a string which is send in only one print statement. And that solved the Problem!!! I had no more hangs since two or more weeks. Even strong polling of my website does not cause any problems.
The only thing is that memory could be too small if you plan to realize a big website. I have a mega 2560, so it is sufficient at the moment.
Regards