A Power of Attorney, like a Trust, does not need to be registered or recorded in the public records in order to be effective. It does have to be in writing, signed, witnessed and notarized. However, once your agent is appointed via a valid Power of Attorney, he or she simply has to present the document at the institution where business is to be transacted on your behalf.
For instance, if your agent needs access to your bank account in order to pay bills on your behalf, he or she will take the Power of Attorney to the appropriate bank to prove that you have authorized such access.
In many situations, a Financial Power of Attorney will authorize an agent to sell property on behalf of the principal (the person who made the Power of Attorney). In this situation, the agent will sign the property deed on behalf of the principal, and the Power of Attorney will be recorded in the appropriate real estate records, along with the deed. However, this is done to show that the agent did, in fact, have authority to sign the deed. Recording the Power of Attorney in this manner does not affect the validity of the document.