Sounds like normal wear and tear, a simple solution would be to just replace the soles, as the rest of the shoe is fine.

As for repair- there are kits to repair soles, however usually they're meant for quick fixes and not to be lasting repair, some searches can show you a few:

http://www.google.com/products?hl=en&sou...

however as stated before, these are usually just for quick crude fixes.

if they are plastic / rubber soles

try a puncture repair kit from a bicycle shop

There is a product just for this purpose ! It was "Bison Marathon", it then became "Bison Liquid Sole", and I think its now called "Bison Liquid Rubber". (Don't they love confusing us ?)

It flexibly fills the hole, and extended the life of a pair of my particular favourite shoes for a couple of years. Make sure the worn part of your shoe sole is as clean as you can possibly make it before applying. If the hole is right through, duct tape the inside first. Their web address is www.bison.net

A similar product is "Shoe Goo"

Try Googling these names for hardware stores in your area.

Another great for rebuilding the soles of your shoes is "Shoegoo Adhesive" which can be found at your local walmart, target, homedepot etc. It comes in a red foil tube and is made by Eclectic Products.