My wife is a postal carrier and will likely retire from the USPS in 2016 at age 62 with 28 years of service. Her pension equals 1.1% of her pay multiplied by years served (about 31%).
Two thoughts here. It's a wonderful source of (not-quite) guaranteeed income, and our goal is to reduce our expenses so much that the hefty reduction in our monthly income will be offset by a much smaller list of liabilities. Combined with SS and a 401K it's a sweet gig. Surely makes all those years in the elements worthwhile. We absolutely have it factored in on the asset side of the balance sheet.
The second thought is if you are one of the few that is still eligible for a pension, pay close attention to how well funded those pensions are. Note the recent developments in Detroit and Chicago. Pensioners in Detroit are about to get a very big haircut in their pensions. The same may happen in Illinois, and other states like NJ and CA are in similar straits. That's why I call it (not-quite) guartanteed income. If you are planning on it being there I would be very mindful that some pensions are much safer than others. The PO should be just fine being under the Federal umbrella, even though they are bleeding cash at the moment, but you just never know....