Forget gas and coal and cotton. Labor migrants are Uzbekistan's number-one export. And new data show their earnings jumped in 2012.  

Russia’s Central Bank says migrant labor remittances sent from Russia to Uzbekistan totaled $5.7 billion in 2012, up 32.6 percent over 2011, when the figure was $4.3 billion. With Uzbekistan's 2012 GDP worth $35 billion (that's the official sum figure converted on the black market), remittances from Russia alone account for the equivalent of 16.3 percent of the economy (if you’re using Tashkent’s official exchange rate, they’re equivalent to 12 percent of GDP).
The Russian Central Bank figures only include official transfers (wired to Uzbekistan via Western Union-type money transfer systems), not cash carried home by migrants. And the figures are only for Russia. So, overall, remittances probably play an even greater role in the Uzbek economy. 
Gas and other energy exports earned Tashkent $5.03 billion in 2012, according to government statistics. (Cotton earned $1.25 billion.)
From time to time Tashkent tries to stop its citizens heading to work in Russia. Authorities never offer a clear explanation why they wish to stop the trend, which is driven by high unemployment at home. But with Uzbekistan’s economy so dependent on migrant remittances, it seems unlikely Tashkent can really afford to stop the human outflow.