A lot of people sure do like to add it, don't they. I'm from the Plain Jane school of "less is more". I've never tried sugar to bump the lather ... beer, yes; sugar, not so much. Never felt the need. I think the way to get an awesome lathering soap is to find the right combo of cleansing (lather), conditioning, and hardness from the blend of oils/fats/butters used.
I'm with you Zany...although when I was a newbie I tried pretty much everything. Guess that's one of the things that make soap making so addicting.
I am not a newbie and some additives make a big enough difference to use them, that I will say my soaps are much better now than when I was a newbie using no additives. There was the time I thought simple was better. Using Chelators and lowering superfat has not only helped slow soap scum it has helped my drains. Using an antioxidant has helps squelch dos in my soaps containing lard and additives such as sorbitol has helped lather without upping CO or PKO, which I keep under 20%. Using vinegar for water replacement or partial water replacement also seems to contribute some to lather but certainly makes a harder soap without the cost of sodium lactate, which I really never have used. Progress can make for better soap
I am not a newbie and some additives make a big enough difference to use them, that I will say my soaps are much better now than when I was a newbie using no additives. There was the time I thought simple was better. Using Chelators and lowering superfat has not only helped slow soap scum it has helped my drains. Using an antioxidant has helps squelch dos in my soaps containing lard and additives such as sorbitol has helped lather without upping CO or PKO, which I keep under 20%. Using vinegar for water replacement or partial water replacement also seems to contribute some to lather but certainly makes a harder soap without the cost of sodium lactate, which I really never have used. Progress can make for better soap
I use the powdered at 1-1.1% of my total batch. You can always play with the amount
Sorbitol is expensive, though I also know it ups lather. Where do you get yours and how much do you add?
It is not cheap, but with my using lower PKO and CO I am finding it really helps kick up the lather. I just de-molded some 50% shea soaps with 10% pko/co split. They already lather well. Usually my shea soaps take a few months to give any lather, now I am not saying it is a lather you would write home about, but it is lather 
