Not so fast, Yahoo! ( YHOO) bulls.

There is a sense that the worst has passed. There is a sense that the page has been turned on an ugly and depressing chapter in the history of the Internet giant.

There may even be a sense of relief over at Google ( GOOG), where the geeks in charge are idealistic enough to trade in a certain monopoly on search in exchange for a sharp competitor who can prod them into developing even better technology.

It would be easy to believe that Yahoo! has turned a corner and that it's all recovery and rallies from here on out. Even after Thursday's tumbling in tech stocks, Yahoo! shares were still about 4% higher than where they closed before Tuesday's fourth-quarter earnings report .

But while Yahoo! has very likely turned a corner, it's too early to get that bullish.

First of all, Yahoo's earnings-inspired 7% surge on Wednesday put it at its highest level since Jan. 18. So if you bought shares last week, went on vacation and just got back in the office today, you could be down on your trade. That's not exactly a rally -- it's more of a short squeeze.

I'm not saying it's over for Yahoo!. I don't buy or sell stocks, but I find myself rooting for or against companies, and I've been rooting for Yahoo! Why? There are a lot of seeds of ideas that could bear fruit for customers and investors alike if they would only take root.

But it's hard for a flower to grow in a pot that's falling from the penthouse window.

And that flower pot is Yahoo!. Not only has the corporate structure been an unsightly shambles that spilled into public view when an executive tried to stage a coup with a rambling memo , but Yahoo! has committed the cardinal sin of commerce: It left money on the table.

It's well known that Yahoo's current search technology has cost it market share, but it has also cost it potential revenue. Page views rose 22% in the fourth quarter, but that was offset by a 3% decline in revenue per page, CFO Susan Decker said. That left search revenue growth "in the high single digits."

Why the drop? According to Decker, it was a "decline in revenue per query in search, which is likely until Panama is fully operational."

In other words, Yahoo!'s delay in rolling out Panama, a technology that can compete with Google's AdWords, is the financial equivalent of Google stuffing millions of dollars into trash bags and tossing them out car windows -- except that it caused fewer traffic jams.

That explains all the excitement surrounding the company's announcement that Panama would be operational ahead of schedule. But it's too late now to get excited about Panama. That moment came nearly two years ago, when it was clear to everyone, including Yahoo! CEO Terry Semel, that Google had surpassed Yahoo! in search, but well before people began to declare Google the winner of the search battle.

It's even too late to breathe a sigh of relief that Panama will finally roll out. That moment came a quarter ago, when Semel swore, with the sweaty earnestness of a deadbeat confronting a bill collector, that Panama would hit the streets in early 2007. All we've heard this quarter is a confirmation that Yahoo! will deliver the goods as promised.

As encouraging as Yahoo! was about its turnaround, it was also sober about how long it will take to show results. In an interview with the New York Times Wednesday, Semel said: "The first time we see any benefit will be at the end of the second quarter. ... Every quarter thereafter we will start to get better."

And as Decker noted, the decline in revenue per query will persist until Panama is "fully operational." Given that even the best-planned technologies suffer glitches and require fine-tuning for a quarter or so, fully operational is something that will happen much later this year. Until then, search revenue could underperform.

That's probably why Yahoo! gave less-than-dazzling guidance despite assurances that the turnaround was on track. Yahoo! said revenue ex-traffic acquisition costs will be between $1.12 billion and $1.23 billion this quarter and between $4.95 billion and $5.45 billion this year. Analysts had been looking for $1.26 billion and $5.47 billion, respectively.

As Larson Kusick observed on RealMoney, several of the most-bullish analysts lowered their earnings estimates for Yahoo! this year following its fourth-quarter report.

There is hope, however, in Yahoo's other revenue generator: display and banner advertising. There, revenue among Yahoo's top 200 U.S. advertisers gained 30% while the dollar-per-display-ad figure also gained. That could offset weak search growth in the near term, but Yahoo! also faces a formidable competitor in Time Warner's ( TWX) Advertising.com.

The good news at Yahoo is good indeed: A long-needed fix is in the works. But the bad news for investors hoping to profit from the turnaround is that they may need to wait several months -- and on the Internet, a lot can change in several months.

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