It was a lot more beat than raise from Nvidia in the chipmaker's third-quarter results released late Wednesday, though there was nothing in the report to suggest that artificial-intelligence mania is anywhere near an end.

There's a lot of talk of bubbles at the moment -- AI, crypto, media companies owned by a particular politician. Joachim Klement, head of strategy at Liberum in London, offers a cautionary tale about the rise of exchange-traded funds. Some, like the ones that track the S&P 500, are broadly diversified and liquid. But many other ETFs are not -- they're thematic and invest in just a small number of specialized companies.