One of the mysteries of DUI sentencing is the requirement of automobile liability insurance after a DUI conviction. Since February, 2008, Florida has required that persons convicted of DUI carry at least $100,000 in bodily injury liability insurance. This is the insurance you buy to pay for injuries you might cause to someone else while driving. In fact, Florida's statutes now require that citizens convicted of DUI carry bodily injury liability insurance of $100,000 per person and $300,000 per incident for personal injuries, and $50,000 of liability insurance for property damage.
Normally, Florida doesn't require any bodily injury liability insurance, but merely requires that every driver carry no-fault, or PIP (Personal Injury Protection) Insurance. However, if you're convicted of DUI, the Florida lawmakers have decided that they want to make sure that you are financially responsible (the FR of FR-44 is "financial responsibility.")
The FR-44 form is merely a piece of paper which states that you have a non-cancellable insurance policy with at least $100,000 in bodily injury liability limits. The form is cheap ($15) but the insurance is not. That's because, in order to make it non-cancellable, the policy has to be paid for in advance--usually six months at a time. Obviously, that is a financial burden that many people cannot pay.
Florida statutes require that anyone convicted of DUI maintain FR-44 insurance for a period of three years from the date that their license revocation ends. (The DHSMV considers this to be the day that you receive a BPO restricted license following a first offense conviction.) Normally, your insurance company will submit the FR-44 form electronically to the Florida Bureau of Financial Responsibility within 15 days of issuing your policy. The Department of Highway Safety and Motor Vehicles will not reinstate your driving privileges until they receive the form by email.
There is more information available here.