We havent had a guitarist's nail thread for a while so I'll start a new one, (old one is here )
I was blessed with fairly strong nails but still had trouble with breakiages and wearing down if I played a lot.
I can't get on with finger picks as they stop you doing down strokes and don't fancy having bits of plastic stuck to my nails.
I started using Hard as Nails (the reassuringly macho nail varnish for men) which worked to an extent but had a tendency to peel off, I think the main benifit was it protected my nails from day to day damage rather than helpd with playing.
I did not screw the top on the bottle properly one day and the stuff started to dry out, being of a thrifty nature I tried to remidy this by adding some nail varnish remover to thin it down again. When I used this I found it worked better and stayed on the nail longer.
After some exprements I find the best thing is; add 12 to 15% of nail varnish remover to H as N then 5 or 6 coats of the undiluted stuff and you can hack away at the strings for hours without peeling, it has added volume to my performance.
What do other guitarists use?