I know I'm coming along late on this thread but I am a nail tech and most of what has been posted on here is correct. For starters, acrylic does not wreck the nail bed. It is improper technique and use of MMA liquid which will cause problems. How to avoid? Do as someone already posted, run, run away from discount nail shops. If they use a dremel tool, and if they will NOT tell you what manufacturer's product they are using on your nails, (and beware if they say OPI because it seems a lot of discount nail salons use OPI Competition 3000 liquid and we know they use MMA). If they don't use disinfected implements, run away. If they pry lifted or broken nails off with a nail tip or anything else (other than soaking in acetone or product remover) run away. I won't go on about this, suffice to say in the nail tech world this is something we are very passionate about. Professional nail techs use EMA liquid, which is more expensive than MMA (which is dental acrylic by the way and NOT to be used on natural nails).
Personally, I wear pink & white acrylic and I keep my extensions short. For those who are asking about gel, I do not find it as strong as acrylic, however it is more flexible on the nail. It is mostly a matter of personal preference. I am hard on my nails so I prefer acrylic. We like to tell our clients that our nails are *jewels, not tools* LOL but in real life we all use them to pry and rip and hold things.
Fungus is not normally something that will grow on fingernails. We see it on toenails often during a pedicure. We usually refer a client with fungus on toenails to the podiatrist/GP before we perform a service on them. What you may see is a bacterial growth under lifted acrylic. This will look like a green/brown spot. It is not harmful, it can be buffed off during your next service. But don't ignore it if you see it. This is all the more reason to ensure you get regular rebalances to keep your nails in top shape.
Hope this info helps - I was actually very pleasantly surprised to read a lot of correct information on this post. There are a lot of myths about artificial nails out there.
Laura