Note that this specifically does not cover a Linux "router", as denoted by the "a bit of clue" clause. Also note that Zebra is stable and useful only when it is doing nothing or next to nothing.
Jumping in over my head: I have both (intel/alpha) Linux boxen running Zebra (for BGP only) with ethernet, T1 and (lanmedia) DS3 interfaces as well as Cisco's ranging from 25xx to 75xx. *nix boxen acting as routers are certainly useful, very flexible and stable when used appropriately. Zebra does basic BGP pretty darn well. OSPF and other things are still broken but the future is bright. I use them and will continue to. They do not compare on the same scale as purpose built hardware and OS's like the Cisco's, Lucent, Ascend... equipment. Anyone that thinks that they compare directly is delusional, as I was.