I have a Mac Mini (Mountain Lion) connected to a WiFi network, getting a DHCP address from the router (ASUS N-16 Tomato).
In addition, I have a headless Ethernet-only appliance (Arch Linux ARM) which can live on the same router using a wired connection - it also gets its address through a DHCP reservation.
What I'd like to do is be able to colocate the appliance with the Mac Mini by connecting it to the Mini's Ethernet port and have the Ethernet port bridged to the WiFi so that the device is completely configured through the router - getting its DHCP address on the same subnet (and not have the Mini doing any NAT).
Just trying to save the extra expense and space of a dedicated hardware bridge, but also trying to keep the network simple. The other routers I have either don't do bridging or they do bridging but are so old that they don't support the latest encryption standards so I'd have to drop my router to WEP. Right now, in looking at the options, if I can't get bridging to work, I'd just as soon get a whole ASUS N-16 and bridge it using Tomato rather than a more limited dedicated bridge/ap, because then I'd have a spare identical router.