At least 30 million.

Whatever number ensures that the company doesn't go on some weird tangent like motion controls. Chasing a new audience and abandoning their fanbase in the process

Why do so many PS360 titles sell below 1m or lets say below 8m (10% of 80m is 8m)?  And especially why do devs still make games then? If you are a smart dev you know that not every system is owned by a potential customer. Some people own more than 1 console. Then there is different age groups. Then there is people interested in different genres and some people even owning a system just to watch blurays (because e.g the PS3 was the best and cheapest bluray player in 2006/7). Also alot of people dont buy mediocre games at all and some wait for price drops or buy used games.  Expecting 10% to buy ones game is pretty dumb unless you are a prestige developer with only great games.

I am not bitter I am just making fun of some devs and I hate shareholders. They fuck up every single company. Everything gets worse because of parasites like them because they dont think "whats best for the company" "whats best for the customers" They just think "whats best for my wallet."  They just care about short term profit and ignore long term profit.
If I would be in charge of a country the first people I would send to a war would be them  (unarmed that is xD)

a tad more than the console you dislike the most.

35M, 20M is too low.

profit is more important than units. How many of the 83million PS3 did Sony sell before they sold one at profit?

The number will be different in each case. Many years ago, Nintendo said in an interview that they have to sell at least 10 million pieces of hardware for a product not to be a failure (it was around the time of the GB Micro's demise).

But this will be different in each case. Sony sold many, many times more PS2's than Nintendo Gamecubes, yet Nintendo posted profits each year. So the GC wasn't a failure in that sense (I haven't looked at detailed financial results to see if the GBA saved them in those days).

Edit: Nintendo recently said that the 3DS' install base is now sufficiently big enough to release more heavy hitting software, and not worry too much about hardware. So you need 40 millions consoles out there before you can start to rest a bit (hopefully they won't). 

Profit is what matters here. Number of units is more irrelevant than most of you think!

Surely that depends on what your goal was before you released your console, surely anything that sells less than your last console, or a console that leaves you with a big reduction in marketshare is a failure.