My neighborhood market is carrying them: think tomatillo, only half the size (or smaller). My Mexican colleague in the office says she has only ever seen them back in Mexico and she isn't completely certain as to their use--though she thinks they would be used just like tomatillos themselves. Everything I've found (precious little, actually) suggests that she's right. Does anyone know whether the tiny ones have a different flavor than their larger cousins--sweeter, smokier, tangier (tangy-er?), etc.?