In my opinion, if you have a well (and even if you don't, in some cases), you need a softener. Sears has a good line of them, I'd definitely buy as opposed to the rent/lease crap that culligan offers. The size you need is going to be determined by how hard your water is, and how much water is used. I have a 27k grain softener in my house, and it does just fine for us, 2-4 people with moderate hardness. You'll more than make your money back in reduced maintenance on things like your washer, hot water heater, dishwasher, plumbing fixtures, soap, etc.
One of my goals in the next few months is to add a softener to my rig.
