Another volatile day of trading, but the result is another day of gains for U.S. stocks, as the benchmark S&P 500 finished up 0.7% on Monday. The narrower Dow Jones Industrial Average (DJINDICES:^DJI) rose 0.6%. Even the technology-heavy Nasdaq Composite Index (NASDAQINDEX:^IXIC), which has been highly volatile recently, managed to gain 0.3%, after having been down close to 2% intraday. The root of the Nasdaq's volatility has been the reversal in momentum in some high-flying "new tech" shares, but two of the best-known "old tech" names, Intel and Yahoo! (NASDAQ: YHOO) provided support to the index in today's run-up to their after-hours earnings announcements. If the after-hours price action is any indication, they'll continue to do the same tomorrow -- Yahoo!'s shares were up 6.5% at 6:50 p.m. ET.

On the headline numbers: Yahoo! beat Wall Street expectations on (adjusted) earnings per share, with $0.38 against a consensus estimate of $0.37, but, more importantly, they beat on revenues for the first time in at least five quarters. Better still, revenues (after traffic acquisition costs, or TAC) grew for the first time in five quarters, albeit by just 1%. CEO Marissa Mayer has now been at the helm of Yahoo! for over 18 months, so revenue growth is a key indicator of the success of her turnaround efforts and is vital to sustaining the momentum of that turnaround. Display revenue ex-TAC rose 2%, while search revenue ex-TAC grew a healthy 9%.

In terms of guidance, revenue ex-TAC for the current quarter is expected to come in between $1.06 billion and $1.1 billion -- in line with the $1.08 billion consensus estimate. The midpoint of that range would translate into year-on-year growth of 0.8% -- meager growth, but growth nevertheless.

Beyond the issue of revenue growth, a major point of focus for investors was Alibaba's results. Yahoo! owns a 24% stake in the Chinese e-commerce company, which is preparing to go public at a valuation that will likely exceed $100 billion. In light of the most recent numbers, that figure now looks more like a floor on the valuation. Yahoo! announced that, in the December quarter (the most recent for which data is available), Alibaba's revenue rose 66%, an acceleration from the 51% growth reported for the previous quarter -- that's a stunning number!

The perspective of an Alibaba IPO has no doubt been one of the factors that has juiced Yahoo!'s impressive stock price performance under Mayer's tenure (the shares have roughly doubled during that period). That's not a factor that is within her control (although the use of any proceeds from a share sale certainly are), but the current quarter suggests her turnaround strategy of small acquisitions to "refresh" Yahoo! and an emphasis on the portal's key properties (the main page and Sports, for example) appear to be gaining traction.

However, the numbers also show that while Yahoo! has improved, the environment hasn't gotten any less competitive -- going up against Google and new entrants, including Facebook and Twitter, remains a very tough challenge.