You're defining a pyramid scheme too narrowly. This is one piece of a pyramid/ponzi scheme, but in those schemes, the underlying asset has no net worth. Here, Evernote clearly has worth, and plenty of it (regardless of whether the exact figure is debatable).

This happens quite often in Series B+ rounds, where previous investors take some or all money off the table. The reason is that early stage investors don't always have the tolerance/portfolio to sustain a long-term investment. Let's use DoCoMo Capital in this example since they were an investor in Evernote's Series A/B rounds. It appears that they didn't invest during this round, so it very well may be the case that they took some of all of their money off the table. It could very well be the case that DoCoMo Capital (who is the venture arm of NTT DoCoMo) made their initial investment in Evernote as a strategic one. Perhaps they no longer see strategic value in the company and need to cash out so they can make different investments that are a better strategic fit for their company. I don't know this to be the case at all - just showing the point.

Alternatively, let's say an angel investor with a very small portfolio had invested in Evernote in their very early stages. It could very well be the case today that 95%+ of that angel's net worth is tied up in the company, and so he/she might want to take some money off the table today to reduce his/her risk.

On the other hand, perhaps Sequoia has the tolerance to wait this out until IPO or a mega-acquisition. So they get in now at a higher price, cash some of the older investors out to reduce some dilution to current shareholders, and then the rest of the cash gets pumped back into the company.

Hopefully this is helpful.