Buyers of junk bonds are loosening the purse strings in a similar way to those in leveraged loans. Last year was the best for risky payment-in-kind bonds (where interest can be rolled up) since 2008, although they make up a smaller proportion of what is now a far larger junk market.
• A boom in flotations is running at a pace not seen since the dotcom bubble burst. Companies are rushing to raise money, and the quality of the protections being offered to shareholders has declined markedly in the hottest sectors of biotechnology and dotcoms. Friday's Alibaba offering, the biggest-ever US IPO, has experienced phenomenal demand for shares that give investors zero say in how the company is run or who it is run by. Shareholders will not even own some of the vital operating assets.
Typically companies choose to sell themselves when investors are overexcited. When a sector is in great demand, entrepreneurs find ways to create supply: more and more companies are created from scratch or carved out of existing businesses until prices tumble. The longer this goes on, the lower the quality of the new companies. Only with hindsight will we know if this has gone on too long.
Read MoreGartman: This is a 'treacherous, nasty trade'
• Alongside the IPO boom, a wave of takeovers looks similar to 2000 and 2007. Takeovers are largely financed by debt, as companies see bonds as even more overpriced than equity, and so easy to sell.
• As companies gear up to buy shares in rivals, they are also borrowing to buy shares in themselves. Both takeovers and buybacks reduce the share count, pushing up prices and making earnings per share grow faster at the expense of the balance sheet.
Overall, Société Générale points out that companies are borrowing more than at the 2007 peak and buying back about the same, although cash flows are a little stronger now (perhaps because super-low rates are keeping down borrowing costs).
Investors are rewarding corporate buybacks. The S&P 500 Buyback index, which measures the 100 stocks buying back the most, outperformed the S&P by 4 percentage points over the past 12 months, about equal to its outperformance in the period up to June 2007, when the credit crunch began – although this is down from the 16 point outperformance last year.