I think I ran into this the other day, but didn't know what it was so it freaked me out. I was going slow in 2wd on wet gravel and approached a steep uphill, 90 degree corner. I turned to power up it and slipped badly enough that I was just going to dig in. I stood on the brake, shifted to 4wd, then reverse for a few feet (so I could engage the 4wd), then back to drive. I then went to quickly transitioned from brake to gas and I got the slippage light and ABS clicks like crazy, then it suddenly got traction and lurched forward. I thought I had tromped on the gas BEFORE it was done engaging 4wd (exactly what I was trying to avoid by reversing until it was engaged...), but Hill Assist makes more sense.

It works fine, but there really should be a separate indicator... actually I'd rather engage it manually.