I love my one pair of addi's too. (Guess what I'm asking for for Christmas? :mrgreen:)
I remember thinking, "How much smoother could they possibly be than other metal needles? I mean, cummon? It's just another pair of metal needles, right?" If you take a strand of yarn and loop it over the shaft and slide it up and down to feel the resistance, you can actually totally tell the difference compaired to regular metal needles like my beloved Boyes.
But as I've said, they're sort of like having satin sheets. A luxury, but I also love my cotton sheet Boye set, and the GREAT convenience of having all sizes with me at all times. Having more Addi's would be a wonderful indulgence though. I've decided to aim to collect a set of 16", since my Boyes don't go down that size, they'll fill in the gap quite nicely.