Now that Carl Icahn and Yahoo! (NASDAQ:YHOO) have made nice, will the peace last? Or is the current calm just the eye of the hurricane?

The one thing investors had better not cling to is the notion that Yahoo! will rise simply because Icahn is on board.

The billionaire investor is a genius, but he's been proving far too mortal lately. Yesterday's Wall Street Journal profiled the returns on Icahn's most recent equity stakes. Those stocks have registered a mixed bag of performance since Icahn stepped in.

Company Date
Acquired
Performance
Since
Acquisition

BEA Systems

8/07

64%

Cyberonics (NASDAQ:CYBX)

11/06

49%

Enzon (NASDAQ:ENZN)

8/07

16%

Biogen Idec (NASDAQ:BIIB)

8/07

14%

Lear (NYSE:LEA)

5/06

(38%)

Motorola (NYSE:MOT)

1/07

(61%)

Blockbuster (NYSE:BBI)

12/04

(72%)

Source: WSJ Market Data Group.

New investors can always take heart that they are getting in today at prices below what Icahn paid to establish his position in Yahoo!, but that consolation may mean little to those who have seen Motorola and Blockbuster continue to plunge.

The attraction of Icahn is that he comes in with a mindset to squeeze near-term shareholder value out of companies. That action sometimes involves pursuing a sale of the company. Sure enough, BEA was acquired three months ago, when Larry Ellison came calling, and that decision proved successful.

However, with winners and losers across the board, it's a better rule for investors to keep an eye on the company than on who's buying into the company.

Some other recent Microhoo dealings:

Biogen Idec is a Motley Fool Stock Advisor recommendation. Try any of our Foolish newsletter services free for 30 days.

Longtime Fool contributor Rick Munarriz is a fan of Yahoo! but not of bad weddings. Hdoes not own shares in any of the stocks in this story. Rick is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.