Here's the other recent thread we had on acrylic nails:
Help: Playing With Acrylic Finger Nails

I believe Murray is/was right about damage. They rough up your nail to put the acrylics on which makes it a bit thinner. If the hard inflexible acrylic accidently pulls off, it can take some of the nail with it. I think this is more likely to happen if you don't get them filled. Mine sure are staying on great, with no problems.

I can't understand how it's possible for them to damage the nail bed. Fingernails themselves don't seem porous - they're certainly waterproof. Also, the nail actually grows from a matrix deep inside the finger. It's covered by tissue and grows out and over the part it's stuck to (the 'underneath' that's visible) but does not grow from there.