With all the environmental consciousness of today, maybe your mother wasn't crazy to wash and reuse the zip-top bags. However, drying those suckers can be a headache. Gaiam sells a counter top bag drying rack
for $19.00 (seen in picture on the right). You can also opt to use chopsticks in a tall glass to create the same system.
Regardless, make sure you clean each bag thoroughly with warm, not hot, water (hot water will warp the bag). Every little thing helps, especially since it takes about 35 years for a single plastic margarine container to decompose.