I have a confession to make, I replaced ALL of the sugar in the chocolate chip cookie recipe with pureed dates. I didn't mean to I was mindlessly going along when I realized I'd done it. The good news was, it really didn't change the taste at all. I thought the texture was a bit bready but no one else seemed to notice.
Ultimately, I think that using half sugar and half date puree would have solved this problem, minor though it may be. When you cream together margarine and sugar you really begin to set the tone for the texture of your final product. Sugar and margarine work together to create these little air pockets that make your product tender rather than bready. Using some sugar would help maintain this tenderness.
I think its probably more important to go this route with comfort foods, like chocolate chip cookies that you're serving for a crowd. I think if you're making chocolate chip cookies for yourself to enjoy and you want a healthier, less guilt inducing option, using all date puree would be fine.
BTW, I've been using organic date pieces in oat flour, the cheapest form of dates I can find, for my date puree experiments. I've been just barely covering the dates with boiling water, covering them and letting them sit a while. Then I puree them and measure out an amount of dates equal to the amount of sugar in the recipe.
I've also measured out the amount of unsoaked dates equal to the amount of sugar in the recipe, covered that with boiling water and pureed just this amount. The dates make such a nasty mess in my Vitamix that I prefer to do a larger quantity at a time and store it in the fridge for a few days.