Acrylic has been the answer for me. My (poor?) technique of attacking the top of my nails on percussive downstrokes was wearing them away quicker than I could grow 'em. A lady friend suggested acrylic was the answer - and I've been attending a local nail salon for two years now, no ill effect, quite the reverse - I have much healthier nails these days.
As others have mentioned - these are not some false layer of material glued on that might 'fly off', but a powder - mixed with solvent - applied by painting on with a paint brush - which sets like glass. Very strong, very durable. As your nails grow a gap appears at the cuticle end which needs back-filling (they call it re-balancing!) - and the number of days before this process needs to be done depends on your diet as much as anything - hence some of the aboves messages mentioning different time intervals.
When I'm eating well (or hitting the vitamin suplements) my nails grow quicker! On avearage I go back every third week - unless I chip one - usually by performing a hard 'straightfingers' into some imanimate object at work!
It costs me £1.50 a nail - and as I use a thumbpick, I only need two fingers doing (poor style once again!) where my pal Alistair Hulett gets a full set ('cept pinkie!).
We both swear by Acrylic - never loooked back.
Cheers! - Duncan