Personally, I use the service on a weekly basis to pay for items ranging from dinner to my rent and have nothing but good to say about it.
In an effort to boost usage, Square is offering anyone who enters an email address on its website a dollar. Requiring some of your personal information in exchange for the dollar doesn't mean it's totally free, but at least the company is paying you instead of a data warehouse.
After entering your email address, you'll receive a message for Square explaining how Cash works, along with directions detailing how to claim your money.
You'll be asked to enter your debit card information so Square can deposit the dollar into your bank account. Going forward, when you use the service to send or receive money, the funds will come out of (or go into) the bank account linked to your debit card. Money is usually deposited into your account within a day or two of accepting the transaction.
You can go to Square.com/cash to sign up for the service and get your free dollar. For those already using the service, unfortunately you don't qualify for the offer.