How many accounts do you have with a single airline?

Some offers, such as the 20K UA visa or the 25K DL Amex seem like they are great ways to get almost free tickets. Do you guys start separate accounts to get these offers (with some, I understand that you can keep reapplying for so the examples above may not be good examles)?

If so, can you combine them & do the airlines raise hell about it when you do?

Just curious...