Taken straight from One Mile at a Time:

For a limited time United is offering their Door-to-Door baggage service for $25. That’s the same price as actually checking the first bag, and cheaper than checking the second bag (for those of you that are stuck paying bag fees).

The United site says this service is normally $79 or $99 (or depending on where on the page you look, normally $149). You’re without your bags longer, but it’s a decent deal, and you don’t have to do the schlepping. Not bad.