For all of those who think TOD is 3 x Alt / 1000 then I hope none of you a) fly high performance unpressurised aircraft and b) have problems with your ears
My aircraft descends at 180Kts = 3nm / minute. If cruising at 12,000ft then by many of the opinions here then TOD is 36nm away. So - you come down at 1000fpm.
If you've got kids in the back, as others have mentioned, they are going to find that a touch on the uncomfortable side.
ROD in that case is the best way to go, and with that in mind a more comfortable 500fpm cruise descent (as I really don't want to replace my IO540 just yet) means the formula is
6 x Alt / 1000 - 72nm.
3 x altitude is great for pressurised airliners or C152's doing 90Kts. It is not a universal panacea as some here seem to think.