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

What: Shares of AOL (UNKNOWN:AOL.DL) have lost about a quarter of their value today after the onetime pioneering ISP reported weak earnings for its fiscal first quarter this morning.

So what: AOL's quarterly revenue climbed 8% year over year to $583.3 million, but the company's adjusted earnings of $0.34 per share were far from its GAAP earnings of only $0.11, which was two thirds lower than the year-ago quarter's result due to various restructuring charges and other one-time costs. Analysts had been expecting $578 million in revenue, but $0.45 in EPS, so even AOL's adjusted bottom line was far below what Wall Street had wanted.

AOL's shift toward an ad-based revenue model continues apace, as total ad revenue was up 16% thanks to an increase of 55% in its third-party platform ad revenue. But its online network of sites recorded a 6% year-over-year drop in ad revenue and overall display-ad revenue fell 3% year over year. The company's haphazard spending spree to drive this shift continues as well, as AOL announced the $101 million acquisition of Convertro, an advertising-effectiveness analytics company in its earnings release.

Now what: For all its efforts, AOL continues to draw virtually all of its adjusted operating income from its subscriber base -- of the $107.3 million in adjusted pretax operating income it reported this quarter, more than 100% came from its subscriber segment. But there are now 9% fewer subscribers than there were a year ago. AOL's attempt to become a content portal has yet to prove profitable, and this latest earnings report only confirms the company's ongoing difficulties. I'd stay on the sidelines for this one.

Alex Planes has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.