The policy is a big issue for anyone who wants to use their phone abroad, without needing to go through their U.S.' carrier's expensive roaming and international plans. Additionally, anyone who wants to move to a new GSM carrier in the U.S. (such as T-Mobile to AT&T), will have issues.
All phones purchased after January 26th are affected, so unlocking all your older phones will not be a problem.
Unfortunately for those who signed the petition, the new policy is monitored by the Library of Congress and "the Library of Congress is an independent legislative branch agency, and it is unclear what power President Obama has to reverse its decision, even if he agrees with the petition," says NPR.