Churchill is Silicon Valley’s answer to the Commonwealth Club in San Francisco or the 92nd Street Y in New York. It is where big names from the technology industry speak, with a heavy bias on local talent. It’s a great venue because the teeming masses of Silicon Valley employees can see legitimate big shots speak. Ballmer has appeared before at Churchill events, always to a packed audience.

I call the choice of Hoffman interesting, fascinating even, because on the one hand he is not a journalist. In other words, he’s not a professional interviewer. Non-journalists typically don’t do a good job of questioning high-power, controversial subjects like the CEO of Microsoft (MSFT). They are usually too polite, too respectful, too timid, too fearful of jeopardizing some current or future business relationship.

The thing about Hoffman — and this is the other hand — is that he’s one of the most intelligent, inquisitive, provocative, no-nonsense luminaries in the Valley. A senior executive at PayPal (EBAY), the founder of the LinkedIn (LNKD), a prominent angel investor, a venture capitalist at Greylock and all-around good guy, Hoffman is more than up to questioning Ballmer the way Ballmer deserves to be questioned. That doesn’t mean he will. (In fact, Hoffman emailed me to say he’s planning to “do a chat that’s business person to business person, not … as a journalist.”)

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Be that as it may, here are a few questions Hoffman might bring onstage with him tonight, whatever role he plays:

* Let’s start with the sudden departure of Windows chief Steven Sinofsky. Did you fire him? Why? Aren’t you concerned it looks bad to have the shepherd of your most important product in years leave three weeks after its introduction? Did Sinofsky leave more because of problems with Windows 8 or problems with Sinofsky? If he was so unbearable, how did you bear him for so long?

Ballmer hasn’t spoken publicly yet about Sinofsky’s departure. (He did send Microsoft employees a pointed memo.) The key isn’t whether Hoffman asks about Sinofsky. The key is how hard Hoffman presses and whether or not he lets Ballmer get away with not answering.

* Regarding your money-pit of an online business, what are you goals? You’ve lost billions? How much more can you tolerate? Is Bing a financial success? Are you satisfied with adding Yahoo’s (YHOO) search business to Microsoft’s? And what’s your opinion of Marissa Mayer while we’re at it?

Hoffman knows the online business as well as anyone. He knows how LinkedIn built a business that by rights should have been offered by Microsoft through its market-dominating Outlook email, calendar and contacts application. A detailed conversation about Microsoft’s shortcomings and prospects here would be fascinating.

* A tough one-liner might be: How come your company’s stock has gone nowhere for ten years? What’s that like?

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* On managing Microsoft, do you have a process (the way your old employer P&G does) for elevating talent and identifying a successor? Is splitting Sinofsky’s job among two people an admission you don’t have the caliber of executive who could do it all? How long will you remain CEO? Also: Microsoft has been notoriously siloed. That has led to some stinging embarrassments such as the Kin phone, which was cancelled — less than two months after it hit the market — in favor of a competing set of internal technologies. How important is cross-pollination and collaboration going to be in the creation of future Microsoft consumer products?

* On games, Microsoft’s Xbox business has grown into one of the company’s most successful and recognizable. In fact, Microsoft has been handily beating competitors Nintendo (NTDOY) and Sony (SNE) for a long time now. What is your vision for expanding the games business to include more entertainment offerings? What’s your take on social gaming, including Zynga (ZNGA)?

* Last, an oddball question … My favorite game (remember, my name is Reid Hoffman), hands down, is Settlers of Catan, a game about stockpiling resources and deploying them smartly. It’s a good game because it combines luck and skill. You can have a lot of skill, but luck can cause the game to work against you — and vice-versa. Steve, do you play Settlers? What’s more important, luck or skill?