Speaking up for the Southeast Region, I have been observing what I believe to be normal population levels of Carolina Wrens throughout the Bootheel and into the southeastern Ozarks; granted, the bootheel didn't receive the amount of snow and cold that the rest of the state experienced.
For the first time since we've lived here (going on 4 years), we have a pair of Carolina Wrens and witnessed them with two immatures taking dust baths in our garden just yesterday evening. I have a stock pile of firewood for my shop's wood stove behind the shop where I think they built their nest.
Would/could some of the more northern populations have moved southward staying in the southern portions until their habitats reach a "normal" equilibrium to which they're more accustomed - regarding Carolina Wrens. I have seen, as a result of a bad acorn/nut crop, a mass exodus of squirrels "migrating" through woodlands and across rivers to move to another area where more food was available. (I kept looking for smoke thinking a fire was behind them. Kind of an eerie feeling.)
Regarding Common Yellowthroat numbers, we also seem to have standard populations in the southeast region. If I focus my attention on Otter Slough CA with a thorough sweep, I generally observe 10 to as many as 50 when birding between 1.5 hours to 3 hours. On 5/31/11 with less than 2 hours spent 20 individuals were observed in the evening. While on 5/26/11, 3 hours in the a.m. yielded a seasonal high so far of 50 individuals throughout the 4866 acres (and yet some areas were not surveyed).