I'm going to be the lone gunman here. I have them and love them. My natural nails grow to be quite wonderful and beautiful looking, but I HATE that nail polish lasts less than a day!!!!!!!!!!!!!!!!! And I really HATE when all of my nails are super long and great looking and then I break one and it looks odd.
The set I have on I got back on MLK day and have changed them once since then. Both my mom and I have had them for years and no ill effects. I get mine taken off more than she does, but still we've had no problems.
Sure when you take them off, yes, your nail will be thin and weak, that's natural. But they do grow back to normal in a month or two.
Also if you go to a good shop that knows what they're doing and takes proper care of their equipment and you don't go sticking your hands in a dish of bateria for weeks at a time, you won't have any problems with them. If you're going to a decent shop and you're a clean person, fungus won't grow under them.
Yes fugus has been reported under some indvidual's artificial nails, which I wouldn't wish on anyone because I'm sure it was a mess to get rid of, but I would first question the individual as to what they did for a living and how they took care of their nails before I go and say the whole idea of artificial is a bad idea. JMHO