A slight amount of
toe-in is desirable in taildraggers, full-scale as well as models, homebuilder's opinions aside. Here's a good article courtesy of DJ Aerotech:
http://www.djaerotech.com/dj_askjd/d...taggerbee.html
Here's the modeling NASA's take:
http://www.nasascale.org/howtos/toe-in.htm
As Don Stackhouse points out, there are so many factors involved: tail area and effectiveness at low speeds, camber, moment arm from CG to mains and tailwheel/skid, vertical CG, etc., that one answer doesn't fit all aircraft.
My Stick-type aircraft do fine with zero or just a little toe-in. My Cubs do really well with at least 2 degrees toe-in. A little positive camber (wheel bottoms closer than the tops) works well for stability also.
We had a guy in the club who let his Cub gear get splayed out (toe-out) from several firm landings, it was very squirrelly as a result.
Obviously, there are many opinions. I'd suggest experimenting a little and find what works for you. I'll bet in most cases it's a little toe-in. YMMV.