The list has another interesting facet: jobs that pay about 30K vs jobs that pay about 100K. And many in the latter category can only be found in big cities with high costs of living. The middle class--nurses and maybe truck drivers, and teachers with more than 10 years on the job--is disappearing. 30K isn't enough to live on, while 100K in San Fran or Austin isn't as much as it appears.