Twitter at its most basic has a product problem and not a revenue or sales problem. I think for product problems founders have a unique perspective and legitimacy to make tough decisions. My guess is that the need for this founder perspective coupled with the fact that Jack was the only founder who was even partially available led to the decision of having him on as part time CEO.

being the CEO of even a small firm is a 150 percent time job.

I still find it hard to believe the Twitter board couldn't find anyone who didn't already have a job.

Yeah it's a pretty bad sign for your company when even the founder is like "this kinda sucks, I'm going to a better company that actually makes money."

As a side note, I have been thinking of Yishan-style CEOs for a while now, with board of directors tweeting often too. Twitter itself would probably be a good candidate for such a public company.