Color, cut, clarity and carat(?). There is actually a rating system VS, VI, ect.....The key to shineys, is having a GIA appraisal. One doesn't buy diamonds to sell......but if you have a GIA certificate and an adequate insurance rider, the stone will never lose its value and the recipient can enjoy it without guilt of financial waste if it is lost. I am fortunate my wife is not a big jewelry hound, but she has a nice shiney for her engagement ring (in a platinum tiffany setting) and matching earrings she got for our 5th ann. That's it other than two nice watches I have gotten her when our children were born. She is extremely practical too, but exercises her very good taste as our means allow.

I've read and can appreciate your frugality posts, but if you had say $5M in the bank, no debt and a mid six figure income, would you drive a 240 D and let coupons dictate where you dined? I have never met any other Germans (my people) that would.