By Steven Eke
BBC Russia analyst
The most important outcome of the government reshuffle in Moscow is that it leaves the world in the dark over who - if, indeed, anyone - President Vladimir Putin has in mind as a chosen successor.
Analysing Russian politics increasingly resembles the Sovietology of previous decades.
Mr Zubkov has been plucked from relative obscurity to be PM
Then, the positioning of Politburo members as they stood on Lenin's mausoleum was seen as a guide to what was happening in the inner recesses of Soviet power.
Now, the promotion and demotion of otherwise rather obscure bureaucrats seems to function in a largely similar way.
Viktor Zubkov's biography contains nothing spectacular. It is the life-story of a solid "Soviet man", who prospered under the previous system and managed to find a niche for himself in post-Soviet Russia.
But the one major achievement is that Vladimir Putin entrusted him with power.
In a system where so much depends on the personal decisions - and whims - of one man, this was critical in bringing him to the prime minister's chair.
All manner of theories now abound as to why Vladimir Putin did not do what many expected and nominate Sergei Ivanov or Dmitry Medvedev, the two men seen as frontrunners in the presidential race, to the premiership.
There has been a concerted campaign in the state media to groom the public image of Sergei Ivanov over the summer.
Although news programmes have long started with a round-up of Vladimir Putin's latest trips, activities and pronouncements, they now often feature Mr Ivanov alongside the president.
The choice of subjects is also revealing: they usually involve materials designed to show Russia as a renascent economic and military power.
Whenever a new weapons system is being tested, for example, it is almost certain that Mr Putin and Mr Ivanov will be there, inspecting it together.
Against this background, the sudden promotion of Viktor Zubkov has caused genuine surprise.
Supporters of Mr Putin have suggested it is because he needs both Mr Ivanov and Mr Medvedev to continue their substantive work during December's parliamentary election, and right until the presidential election next March.
Critics of Mr Putin say it is a sign of panic.
They point to how a recent attempt by his spin-doctors to cast him in the image of a "tough guy" - shirtless photos, noticeably bulked-up muscles - backfired, with many Russians suggesting he had all but given up on real politics.
Keeping the world guessing, the critics' theory goes, is meant to suggest Mr Putin is anything but a lame duck.
Mr Ivanov has often been seen with President Putin recently
An alternative explanation suggests that the early promotion of Sergei Ivanov would send the wrong signals to the West, a day after Russia claimed to have exploded the world's largest conventional bomb.
Mr Ivanov has made sometimes very blunt comments about Russia's relations with the outside world.
Finally, there is the notion that there is serious infighting between Kremlin "clans" over the successor, and the appointment of Viktor Zubkov helps keep a lid on something the public is not supposed to see.
It has long been accepted that there are sometimes mutually antagonistic groupings inside the Kremlin, with varying degrees of access to the president's ear.
Many analysts consider its most anti-Western elements to be behind the deterioration of Russia's relations with the West over the last two years.
Vladimir Putin personally retains a degree of popularity and trust unthinkable for most Western leaders and, indeed, for any of his opponents at home.
However, there are many Russian analysts who challenge the notion that Russia is more stable under his rule.
They have suggested that his departure might reveal that the system is anything but stable, and that the forthcoming parliamentary and presidential elections are likely to produce many surprises.