I haven't withdrawn in USD yet, not sure there is a limit for verified accounts, but, I can tell you the deposit amounts:
Via electronic check, "Green" or "BillPay": Min $50.00 max $5000.00
Via Personal or Company check: Min $200.00 Max $20,000.00
They also require you to "verify" your account if you want to trade in USD. A minor pain but, I can understand it from their point of view.