well if he plans on keeping long time storage of stuff, instead of backing up on another hhd, i would have him invest in a cd/dvd burner. it was the best investment i have made. i keep everything from files to music to movies to entire backups of hhd's backed up to cd's and dvd's.
but if he's using the hhd for backup's and short time storage, then the extra hhd would be a good invest. i would shop around though, and get reviews on products. i have heard that raptor hhd's are good, but i have never used one.
although they are a little pricey, this the link below is just an example, and not meant to be that perticular site to buy from.