I've been on the board of Letslink UK - which has kept the LETS flame burning in the UK for many years -for a while now, and it's only recently I've worked out why LETs don't scale.

LETS involve monetising credit (which is what Banks do as well), and rely upon trust. That's fine among communities where trust is normal, but once the "commercial" world is involved, trust goes out of the window.

As Comrade Stalin said:

"Trust: but Validate".

"The future is already here -- it's just not very evenly distributed" William Gibson