medic,
As you said, many have started out with Firebirds or Aerobirds with great success. (I'd suggest the Aerobird to anyone seriously considering a smallish electric, becasue they're 3 channel and a bit more controllable.) And as Dave Segal said, virtually any plane can be powered successfully by electric power today, and perform very well. In fact, if you're willing to invest $700 to $1000 in the power system, you can put together a 40 size plane that will outperform it's glow powered counterpart with a 60 size four stroke, both in power and endurance.

I have, and fly, smaller electrics up to speed 400 size and enjoy the convenience of electric power, BUT they will likely not replace internal combustion engines for me anytime soon. There IS nothing like the sound and pure testosterone grunt of glow and gas.
Dennis-