Take the costs associated with refinancing (everything from origination fees, appraisal, document fees, etc) vs. the monthly savings and see how long it will take you to make your money back (then compare that with how long you plan to be in the house). Don't forget that if you roll the costs into the new loan you will be paying interest on those costs (all the more reason to be wary of 'garbage' fees and inflated expenses).
There are some very good rates out there - I am refinancing a property myself at the moment and rates are very good on 30 year conforming loans. You can already see some of the effects of the sub-prime mess though, so don't expect to find many good deals on variable rate or interest-only loans.