There are concerns that the PET/PETE 1 bottles (which is what most plastic beverage bottles are made of) breaks down much as the polycarb does.

I personally use the PET/PETE 1 bottles for making sports drink from powder (for electrolyte replacement) but then throw them out after a use or two. I like doing it this way because 1) I don't have to risk getting sticky crap in my good water bottles, and 2) I minimize the risk of ingesting chemicals that have leached into the water.

Also with powdered sports drinks, don't leave them in the sun and heat on multiple day trips. Let's just say they get a little "fragrant." All the more reason to use the cheapies for sports drink and save the good ones for water only.