I've run into issues importing contacts using the exported file from the CRM being used. Those issues aside, it seems like the import process for contacts should include an undo option. In other words, if the import has unintended results, you should be able to revert.
In addition to this necessary feature, I want to echo other posts that have raised the idea of allowing mailing addresses to be imported. Mailing addresses are available fields if you manually add a contact. It seems that a mailing address should also be an option for importing contacts.