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 online brokerage E*TRADE Financial (Nasdaq: ETFC) were soaring today, gaining as much as 18% in intraday trading on heavy volume.

So what: E*TRADE is scheduled to report its earnings after the market close today. Right now though, shareholders could give a hoot about that report. In an SEC filing today, E*TRADE disclosed a letter from its largest shareholder, Citadel. The letter broadly criticized E*TRADE and, in particular, its board, for missteps over the past few years in managing E*TRADE's balance sheet, keeping up with competition, and protecting its brand value. The hedge fund suggested that the company hire an investment banker to explore a sale, eliminate its staggered board structure, and remove two of its directors.

Now what: Based on this letter, Citadel is hopping mad. However, company boards have been known to fail to act even in the face of solid logic and heated investors. So while today's big jump suggests that investors are optimistic that the company will sell itself -- and get an attractive price -- that outcome is very speculative at this point.

For current investors who have been frustrated with the company's performance, the push from Citadel could be really great news, and it seems well worth sticking around to see how this shakes out. However, for those on the sidelines, I'd caution against jumping on E*TRADE's stock solely as a bet on a sale.

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Fool contributor Matt Koppenheffer does not have a financial interest in any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or Facebook. The Fool's disclosure policy prefers dividends over a sharp stick in the eye.