I'm with Paul on this one. Personally I don't like installing oak worktops because people don't maintain them and if wet steel/cast-iron pans, knives or utensils are left on them in an area where the finish is thin or absent you can get indellible black stains (ferric oxide, caused by reaction between tannin in the oak and iron). This stain can be removed by judicious use of oxallic acid before refinishing, but nonetheless there are some households where I seem to have to go back regularly to correct this problem. Walnut and mahogany (both species with high tannin content) also suffer from this problem
If your friends are prepared to maintain the worktop and treat it with care by using a drainer, wiping spills immediately and oiling it regularly then it will probably be all right. If they aren't prepared to put the work in to maintain the top then they simply shouldn't be considering a timber worktop at all
Scrit