A sailplane has very high aspect-ratio wings and can have a glide ratio up to 70:1 (the wing L/D ratio is even higher since the fuselage adds drag).
The flow at such high L/D ratios for such long, thin wings approximates 2D potential flow.
Potential flow is how an idealized zero-viscosity incompressible fluid flows. There is no energy dissipation and zero drag. The flow-field has no curl (shear stress is needed to rotate a fluid parcel, which requires viscous shearing on said parcel) and no divergence. This greatly simplifies fluid dynamics calculations and is useful as a conceptual first approximation.
In 2D potential flow lift is proportional to the circulation around the object and the airspeed of the object. Circulation can be thought of as the total amount of curl in a region: the curl in some sense is "concentrated" at boundary of the air foil. Since the vector field is curl-free everywhere else, any curve drawn that goes around the airfoil will have the same circulation.
Any value of circulation can be plugged into the potential flow equations; it is a free parameter. In real life however, viscosity is used to generate circulation. The most obvious way is to drag air around a spinning cylinder. Since potential flow ignores viscosity, it cannot differentiate between a non-spinning cylinder and a spinning one. But real fluids can.
Airfoils also generate circulation. Trailing edges of airfoils generally point downward with respect to the air-stream, even at zero angle of attack (due to camber). Suppose a glider with very long wings is in still air and is suddenly launched. The flow around the wings initially has zero circulation. But (I think) this is (very roughly!) what will happen: drag from the airfoil will tend to slow down fluid parcels that pass near it. But the trailing edge is tilted downwards, which means that it is initially sheltered somewhat from the airflow and generates less drag. This asymmetry in drag will induce a circulation that speeds up air passing over the top (and slows down air passing over the bottom). Eventually an equilibrium is reached; the Kutta condition gives a simple way to estimate this equilibrium circulation.
This is my valiant attempt to unify three explanations of lift: Newton's "deflect air down", Bernouli's "moving faster = lower pressure" and "potential circulation but with a little viscosity". But there is little drag to get this process going. Naively, I assume that wing with an L/D ratio of 100 must travel 100 times the it's chord before the lift is "fully" built up. Is this intuition (backed up with crude experiments dragging a flat plate through water at an angle) correct?
A symmetric airfoil at zero angle of attack generates no lift. If my reasoning is correct, coating the top with shark skin to reduce drag should cause such an airfoil to have a positive lift.