I looked into this recently.

If you take a distribution from your "after tax" savings, you must:

1) Pay ordinary income tax on the gains, and the gains are prorated for how much you take out.

and, here's the kicker:

2) Pay a 10% IRS penalty for any distribution prior to 59 1/2 years of age.

If you call Vanguard and ask to take some out, they will read a required statement where they warn you about the 10% penalty. I was getting ready to buy some land to diversify when I learned about the penalty and elected not to do it.

So, if you are older than 59 1/2, this might be good, but if younger, you are going to pony up 10% to the IRS.