For short periods of time it's ok to store cigars in zip lock bags.
For long term storage it's not so good.
Cigars need to breath to age.
Air exchange is vital to the proper aging of cigars.
This is actually sort of in contradiction to what many serious Habanophiles regard as ideal long term storage.
1. Ziplock storage bags slow down the transpiration of gases and moisture from the cigars within to the environment outside the bag.
2. Reducing exposure to oxygen will slow down oxidative chemical processes integral to tobacco maturation (i.e., aging).
3. Air exchange is a given for any storage system other than airtight, impermeable containers (e.g., glass jars, sealed metal tins). As such, air (or specifically the oxygen contained therein) is implicit in the aging of cigars.
So for long term storage (years to decades), ziploc bags (or any other container that cuts down the oxygen access) are actually beneficial in terms of minimizing degradation over long stretches of time.
However, since aging is slowed, that means that if one enjoys the profile of cigars that have some age on them, then one would have to wait that much longer to enjoy them. For example, if you prefer cigars with 5 years of age, then for cigars stored in an airtight container, you might have to wait 10-20 years (I pulled these numbers out of thin air) for the same profile.
Wilkey