Never liked it myself. Some of them smell OK in the container, but get way too overpowering once sprinkled over the carpet. And even with a clean dust bag, once it's been sat in the cleaner for a few days, the scent seems to alter and becomes rather unpleasant to my nose.
Having only tried it on a few occasions, I couldn't say for sure either way whether or not it damages vacuum cleaners over time, so will trust the judgement of the experts on this one. What I do know is that the brushroll, air paths and bag compartment all get covered in a white, powdery film. Any time I receive a used vacuum in this condition, it gets stripped down fully and scrubbed inside and out to get rid of the mess.
A little scent is OK by me, so I do sometimes use drop-in bag fresheners. Oreck original Fresh Air tabs are my current favourite, and have a pleasant rose scent. Sebo citrus capsules are good if you want something a little stronger. What I really miss though are the little green fragrance capsules Vorwerk used to sell. Smelled fantastic, but I've never been able to find anything even remotely similar since they were discontinued and replaced by the square Dovina chips.