It's difficult to talk about suspension through the internet because there are so many different factors that can affect the end result: toe, camber, caster, ackermann, scrub radius, tire pressure, tire construction, spring rates, roll center heights, dampers, etc... The suspension as a whole is a complicated system that works as a complete unit and any change to one aspect usually affects the others.
But getting back to toe: I agree Old Guy that toe-IN can improve straight line stability compared to toe-OUT which can follow the road imperfections. However, consider that tires do not generate lateral forces (grip) until the tire twists and deflects with a certain amount of slip angle. Since the outside loaded tire does most of the work in changing the direction of the car, toe-OUT has the outer tire pointing in the opposite direction of the turn.
Let's say there is 1 degrees of toe out per side. The outer tire needs to turn 1 degree just to be pointed straight, which does not contribute to lateral load generation. While the inner tire is now at 2 degrees, its contribution to directional change becomes ever less significant as weight is being transferred off of it and to the outer tire. As the outer tire gets increased load and builds up to 2,3,4...7,8,9 degrees of slip angle, it generates more and more lateral load.
For toe-IN. Lets say both tires have 1* of toe-IN. In this case the outer tire has 1* pre-loaded in the direction of a turn. As the car steers 1* into the corner, the outer tire increases to 2* of slip angle and deflection as load is being transferred to it, while the unloaded inner tire is now at 0*. At this stage, the toe-IN example has 2* of steering input from the outer LOADED tire and 0* on the unloaded inner tire (compared to the toe-OUT example where the outer, loaded tire is at 0* and the inner unloaded tire has 2*). The ideal, peak slip angle of, say 10*, for a tire gets there quicker in the toe-IN example.
So, why not always run toe-IN?
Depending on many of the other factors in the suspension, the improved turn-in response and 'pointy', 'direct', 'twitchy' feeling of toe-IN may not be desirable. Also the effects of toe can vary with speed and as said in my previous post, toe-OUT can contribute to more front grip steady-state than toe-IN. Also the improved turn-IN response of toe-IN becomes more significant at higher speeds, but also builds up to the steady-state understeer quicker.
For autocross, toe-IN would probably not be good, while at a track with high speed esses and transitions where the car needs to change direction quickly but settle to a (relative) steady-state understeer, toe-IN might be more desirable. It all depends on many factors and its difficult to give blanket statements for anything due to all of the variables in the suspension system. However, if a car oversteers at the limit but feels lazy from initial turning response, toe-IN might be a good direction to try. That or stiffening the dampers, front swaybar, or various other changes...
darock - where do you notice this 'floaty' feeling? Does it get worse the faster you go? Is it bad when going down a straight road, bumpy road, or when initially turning in corners?
