Even a few ppm of hardness can negate the "slippery" feeling. Also other minerals in water can also affect this. I would recommend you get a simple soap test kit to determine if your softener is working or a Hach 5B.

1 GPG which is considered "soft" is actually 17.1 ppm of hardness.

I installed(2011) my water softener shortly after removing the hard water build up that was even with the bottom heating element. Only replaced the elements(didn't know about the anode). 50gal U.S.Craftmaster hot water tank Installed 4-17-06. No maintenance to the hot water tank after the softener. This is for anyone trying to claim a water softener shortens the life of the tank.

I didn't clean my softener yet reach4...I did do a hand test to see how much has built up over the years in my tank. I would say between 6-7" has accumulated at the bottom over the years from what doesn't dissolve from the salt I posted.