Got my new E4200 set up last night, replacing my trusty old WRT54GL w/Tomato 1.28.
Everything works fine, GUI config was responsive although less well-organized. Most of the features I need such as static DHCP, QoS for prioritizing VoIP traffic etc., is in the stock firmware. Guest SSID is a bonus, but not really needed. Performance for the G devices that I have showed some small improvement in terms of increased signal strength (80% to 95%). I checked the 5GHz N signal across the two opposing corners of my house (about 40 feet apart on two separate floors with 3 walls in between) using a Lenovo T61P notebook. It was 3 bars, 45-60Mbps sync rate, and around -65dBm (according to inSSIDer). So, not too bad.
What I really missed in Tomato is the bandwidth meter and log. I wonder what would it take for TomatoUSB to support the E4200, and if there is something I can help with?