U.S. Census data show that there were 16 cities that, as of the 2000 Census, had a minimal population of 300k and a maximum of 399k.  By official count, Oakland had 399k people and Tampa had 303k.  Pittsburgh fell in the lower half of the group with 334k. 

What happened a decade later to this group of 16?  Pittsburgh lost 9% of its population and now stands at 305k.  Oakland, St. Louis and Santa Ana likewise lost population but stayed within the range of the group.  Two Ohio cities, Cincinnati and Toledo, lost population and now cover fewer than 300k people, removing them from the cohort.   

Three western cities-Mesa, Colorado Springs, and Omaha-added population and currently have more than 400k, removing them from the group.  Miami, Anaheim, Tampa, Wichita, Minneapolis, Arlington, and Tulsa either added population or remained flat but remained in the 300-399k range a decade later. 

As of the 2010 Census the new 300k club, based on the changes of that original group, has 13 members: Miami now tops the list at 399k and Pittsburgh is at the bottom of the bracket with its 305k population.  With the departures of Mesa, Colorado Springs, Omaha, Cincinnati, and Toledo the group shrunk to 11: population losses in Cleveland and New Orleans pushed them into the cohort.