Nearly always a draw or 2nd pair in my experience. 9 times out of 10 they fold to a raise, not entirely sure what they're hoping to happen with their retardedly small donkbets.
This is the most infuriating tactic at the micros.
That may be exactly the goal, can you say mini TILT. Over thinking, monsterflop, SNAP YOU OFF!!
2x at higher levels is semi standard, I try to not play more aggressive just because it's micro!! Or that's just me!!