The US is still the world's largest economy and home to some of the world's best companies and a huge array of investment opportunities in real estate, fixed income, equities and other assets. And just about everything is denominated in USD which, in spite of the best efforts of the Federal Reserve and successive administrations of spendthrift politicians, is still the world's reserve currency of choice.
It's a great place to invest but non US-persons should take the time to familiarise themselves with an egregious provision of US tax law. US citizens get a lifetime federal estate and gift tax exemption USD5.49 million for an individual. For non-US citizens the exemption is USD60,000 – most US situated assets will then be taxed at the relevant rate of estate duty which is currently 40 percent. They will also have the not inconsiderable pain-in-the butt of having to fill in and file the US's typically mind-numbingly confusing returns with the IRS (and possibly state authorities as well) and may well need a lawyer to handle the paper work.
A simple example: If I purchased a property in the US for USD1.0 million in cash today and died tomorrow, my estate would be faced with a USD376,000 federal tax bill even though no profit or gain has been made on the investment.
Two useful plain-English links:US Tax 1 and US Tax 2 are provided with a laundry list of disclaimers including that I am totally unqualified to advise on tax laws (or anything else), that I do not endorse the information in the links and that the information should be checked to see if it is up to date, correct etc.
For my purposes, the risk of my heirs receiving an unexpected tax bill can be mitigated by not investing directly in the US. For US equities, I would invest in a non-US equity fund and for real estate, I would invest through an offshore company.
Unfortunately, I did not become aware of this until after I had invested in some land banking syndicates. They're in Mrs Traineeinvestor's name so I've made it clear that she is not allowed to die until after we have fully exited. I've also made the decision not to add to our existing investments in this area.