By popular request, here are the Rules of Scotch, as defined in Down From Ten. According to Carol in the book a good scotch:
1) Must be unpolluted (served neat–no water or ice)
2) It must be individualistic (single malt only–no blended scotch)
3) Must be bold (i.e. distinctive flavor character)
4) Must be as mature as you can possibly afford, and under no circumstances may it be aged fewer than 12 years.
5) Follow these rules, and you will never have an unpleasant experience, except through overindulgence.
Of course, in the book, the entire thing is couched in an elaborate and highly disturbing dirty joke which makes it much, much more memorable.
Stripped of the joke, though, they are a good guide for choosing good scotches in the absence of other evidence. More advanced Scotch drinkers know that there are some spectacular 10-years out there, but there are also some really awful ones. The same is true for blended scotch–some of them are wonderful, most are mediocre, and a few are god-awful. 12-years and up, single-malt with a good sense of itself is the most reliable way to go.
Thanks to Puck Malmud for the prod on this one