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The limit is $10k, and has been for some time, all transactions that size or higher are reported to the UST/IRS.
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But don't assume that if you transact under $10k, you are flying under the radar. There are two forms... one for ALL transactions over $10k:
http://www.fincen.gov/fin103_ctrc.pdf
And one for "suspicious" transactions, in aggregate, over $5k:
http://www.fincen.gov/fin102_form_only.pdf
Note that both are casino-specific. Casinos and card clubs are targetted. You might want to read the instructions to this form to educate yourself about the rules for filing Suspicious Activity Reports:
http://www.fincen.gov/fin102a_instructions_only.pdf
Also note that the feds are leaning on casinos to file these SARCs, and it's somewhat common to be questioned at the cage when cashing out even a few grand.
Also, what you called smurfing, the documents officially term "structuring." Just so you know what that term means if you see it.