Q. Do I need to have the IRS Form 2848 notarized in order for it to be valid?
No. Form 2848, which allows you to authorize someone else to represent you before the IRS, needs to be signed by the person (or representative from a business entity) but does not need a stamp from a notary public.
NOTE: This is my understanding of current U.S. tax law. Things do change, so call the IRS at 1-800-829-1040 to confirm.