Since it hasn't been around for even a decade yet perhaps it's too soon to tell. That being said, however, you would be hard put to find anyone who will say they've experienced anything harmful due to their use. Some people may find that they are allergic to PG and need to switch to VG based juices instead. Then there is the dreaded dry mouth, and some say they have developed incredibly fragrant flatulence, lol. You can read more in the
Health, Safety and E-Smoking section.
As for benefits, all the ones you mention plus all the benefits of just quitting smoking of course. Then there is the thought that PG may be a potent anti viral/anti bacterial agent. Many of us who've vaped for a long time have noticed we hardly ever, if at all, even catch the common cold any more. I used to get a cold then bronchitis and possibly pneumonia twice a year atleast. In the 2+ years I've been vaping I've got one cold that lasted for 3 days, very mild symptoms, no lasting cough. I think that's amazing!