As of 2010, if you paid $600 or more in mortgage interest payments, the lender must issue a Form 1098. You use the information from Form 1098 to prepare IRS Schedule A—Itemized Deductions. You should receive the form by Jan. 31 following the tax year. The lender will submit a duplicate copy to the IRS.
If you're not itemizing or if taking the standard deduction is better for you, then no, you don't have to enter the interest you paid.