Connection problems with Intel Centrino Advanced-N 6230 and Linksys WRT54G router

Using my new Dell XPS 15 (LX502) with an Intel Centrino Advanced-N 6230 wireless card I couldn't connect to my WRT54G router running the Tomato firmware anymore. Neither WPA nor WPA2 worked, not even WEP. Turns out that I had "Afterburner" mode enabled, which seems to cause problems, as also described here. After disabling this feature in the Tomato interface, everything worked nicely again.