I haven't poked into this thread in a while but I just wanted to add something to the Mashed potatoes with Mayo talk.
Butter isn't something we have on hand regularly here, so years ago I started making mashed potatoes with Mayo.
I don't know about creamy-er but they are certainly creamy. I don't care for the flavor of Mayo though, so I began only using that method when I was making Ranch-Mashed (Mashed potatoes with some ranch dressing mix mixed in)
I have since replaced Mayo with fat free Cream Cheese! A little splash of skim milk and about half a box of FFCC, dash of sea salt, dash of fresh ground pepper and a few dashes of parsely. It's definately my favorite way to make mashed potatoes now. Super creamy, delicious and less fat/cal than butter OR Mayo and another way to sneak more protien into my growing boys