I live in Florida and mail checks to IB in Connecticut. I consistently get an E-mail from IB at about 4pm, 3 days later, advising me of the receipt and the date my funds will be available. It seems to work flawlessly so long as you print out the deposit notification form and send it in with your check.
Here in Canada it was too difficult and expensive to set it up that I could wire funds to IB. So I just got a bank draft made out to Interactive Brokers, wrote my account number on it and mailed it to them with a deposit slip. I mailed it on Wednesday and it was in my account by Friday.