I have seen several tutorials that use piping gel to attach pearls and fondant pieces, make waves, etc. to cakes.  Does Piping Gel ever dry to where it is not tacky?  

I wouldn't use piping gel. I would use melted white chocolate (preferably, it solidifies quickly) or royal icing.

I remember my first pearl cake...I didn't use ANYTHING to attach the pearls...that was a learning experience! I agree with shanter, use melted chocolate or royal icing!

Oh...and BTW...I don't think piping gel ever dries solid...at least it hasn't in my experience, but I've only used is for water scenes and such and I've used quite a bit...so maybe it does dry solid after a few weeks...