I recently found out about Vanguard's Total World Stock Index Fund, a cap-weighted index of the whole world's stock markets. I like this a lot, it's an appealingly simple way to get the maximum possible diversification.
The only thing I hesitate over is that it's about a 60/40 ratio of US to international. Until now, I've been holding VTSAX/VTIAX at more like 75/25.
Based on
this Bogleheads thread, investors have historically fared best with a larger tilt to U.S. stocks. But past performance is no guarantee of future results, and if you asked me whether the U.S. was headed down a path of long-term decline, well... given the political situation, I couldn't say no with any confidence. Plus, U.S. stocks are pretty expensive right now, so maybe buying more international stocks is a relative bargain.
What are the rest of you clever Mustachians doing? Do you hold VTWAX? If so, how much?