My home loan has interest at the rate of 6.125%. With interest rates dropping, is it worth it to refinance?

I am beginning my 4th year of a 30 year term home loan at the rate of 6.125%. With interest rates dropping, is it worth the time and expense to refinance to get a newer and better interest rate? If so, what rate would be considered "worth it"? http://bit.ly/kigB3r