Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

This year has already seen more than its fair share of winning streaks in the stock market, but September's seven-day streak ended today with the S&P 500 (^GSPC 1.20%) losing roughly a third of a percentage point, while the narrower, price-weighted Dow Jones Industrial Average (^DJI 0.69%) fell 0.2%.

Consistent with those small losses, the CBOE Volatility Index (^VIX -7.38%) rose 3.4% today, to close at 14.29 -- the VIX, Wall Street's "fear index," is calculated from S&P 500 option prices and reflects investor expectations for stock market volatility over the coming 30 days.

Facebook is so 2012
From the last blockbuster technology initial public offering (IPO) to the next one.

Just one day after Facebook's (META 2.98%) shares achieved their highest intraday and closing price since their first day of trading in May 2012. Twitter announced today that it has filed a key document in anticipation of a public market listing; the micro-blogging platform broke the news with -- how else? -- a tweet:

Perhaps you're wondering what Twitter meant by "confidentially" -- didn't that very tweet disseminate the news far and wide across the web (as I write this, it has already been retweeted almost 10,000 times)?

In fact, the company is referring not to the act of filing but to the document itself, which was submitted under the Jumpstart Our Business Startups or JOBS Act. The act, which passed into law last year, enables businesses with less than $1 billion in annual revenues to keep their securities filings under wraps until three weeks before the start of an investor roadshow.

Over the past several months, Twitter has been actively looking at different ways of boosting revenue in the run-up to a share flotation. Just two days ago, the company announced its largest acquisition to date, that of MoPub, a mobile advertising exchange that serves up 2 billion ads a day across a variety of websites, including Twitter. MoPub will improve the ad-buying process on Twitter by enabling companies to reach specific groups of users in real time.

As MoPub's name implies, "mobile" is where it's at -- for both companies. Or as MoPub's CEO Jim Payne put it in the press release announcing the deal, "Like MoPub, Twitter has been 'mobile first' since their inception, which makes our two companies a natural match."

Facebook's stock has rallied more than 60% since announcing in July that ad sales on wireless devices are on track to exceed those associated with desktop computers. In the run-up to its share offering, Twitter knows full well on which side the bread is buttered.