A steep stock run-up like eToys experienced creates a class of huge winners.

Still, some analysts also said that the announcement was not quite enough to justify the large stock run-up.

The stock run-up may also have put some investors' asset allocations out of whack, making a rebalancing of their portfolios necessary.

The stock run-up of UAL has come amid speculation that a bidding war will break out for the company.

For one, don't get too excited about the recent stock run-up.

Any further stock run-ups, Mr. Henwood warned, could force the firm to hold back the release of its reports.

And the stock run-up caused at least one Wall Street firm to make a cautious move.

While speculators have profited from these stock run-ups, though, little if any tangible benefit has flowed to the companies themselves - until now.

Another advantage to this approach is that it avoids market timing, meaning that long-term investors don't miss out on stock run-ups.

Amylin's stock run-up has more to do with investors' anticipation of its second diabetes drug, exenatide, which analysts expect to win approval by April 30.