Can I add many customers to a customer group at once?

At the moment customers are assigned to a group one at a time from their profile:

1. Go to Customers → Manage Customers and open the customer (use Search customers… to find them fast).
2. On the Profile tab, choose the group in Customer Group.
3. Click Save changes.

The Assign customers → link on the Customer Groups page takes you to the customer list for this. The Members column on Customers → Customer Groups shows how many customers each group has, so you can check your progress.