Check 21
The Check Clearing for the 21st Century Act (Check 21) was signed into law on October 28, 2003, and became effective on October 28, 2004.
Check 21 speeds up check processing by creating a new "negotiable instrument" called a substitute check, which would permit banks process check information electronically, and to deliver substitute checks to banks that want to continue receiving paper checks.
In short, if you are used to paying for groceries on Wednesday with the assumption that it won't get to the grocer's bank till Thursday, and won't get to your bank until Friday after you cash your paycheck, assume no more. Check 21 allows for the paper check to be made electronic, leader to faster payments, but reducing/eliminating your ability to float checks.
Another problem with the new law include the fact that though checks will clear faster, banks have no increased obligation to make your money available to you.