Just on Tuesday, Bill Ackman resigned from the JC Penney board after losing a high-profile feud. That stock sank nearly four percent. BeaconLight Capital separately criticized retailer Jos. A Banks for not returning cash to shareholders and said it should reorganize its board, a move that sent its stock up more than 12 percent. And to cap a day of excitement, Carl Icahn announced, via twitter, that he had bought a sizeable stake in Apple and was talking to CEO Tim Cook about a bigger share buyback program. Apple flew nearly five percent on the news.
(Read more: Carl Icahn says he's taken a position in Apple, says stocks undervalued)
Wednesday will be a busy day for activists, since big shareholders have to file their second quarter holdings with the Securities and Exchange Commission by the end of the day. Appaloosa landed its filing after the bell Tuesday, showing its Goodyear stake grew to 22 million, up some 6.8 million shares since March 31. That stock jumped in afterhours trading.
Experts who have followed Icahn say he' s one of the stronger names to follow. Many times activists don't immediately reveal their holdings but work on a relationship with management to extract changes. Icahn, however, has made it clear what he wants from Apple- a bigger share repurchase program. Icahn's other holdings include Herbalife, up 96 percent year-to-date; Netflix, up 180 percent YTD; WebMD, up 131 percent YTD, and Federal Mogul, up 114 percent YTD.
(Read more: Apple sets iPhone launch date, Wall Street says buy now)
Charlie Tian, founder of Gurufocus.com, said Icahn typically makes out well on his larger holdings. "Not all of them go up but the important ones, the big ones go up," he said "His second largest holding is Chesapeake Energy. He gained 40 percent on his position."
Tian said he started the Guru tracking website after he made money following big investors in the late 1990s. A physicist by trade, he had started making big gains trading in the tech bubble.
"If you follow the ones with the most steady performance,you will actually do well," he said, mentioning Buffett and Third Point's DanLoeb. Tian said Apple should do okay with Icahn in the picture.
Stone has long been interested in the activity of investor Warren Buffett, and said some investors might follow Buffett as a strategy.
"But he is more difficult to follow now that he will buy a whole company rather than stocks," said Stone.
Some companies that undertake buybacks actually do more harm, Tian said. "If you buy back an overvalued stock back, in the long term,it doesn't benefit the shareholder," he said. "If you buy an undervalued stock,it benefits shareholders, and I think Apple at its current price benefits shareholders."
He said the Ackman's foray into JC Penney is a very different story. JC Penney fundamentals don't look that good, and stocks like that don't necessarily improve because of an activist investor. "The ones under financial stress can go either way," Tian said.
Citigroup retail analyst Deborah Weinswig, in a report Tuesday, said it wasn't clear what the point was behind Ackman's battle to remove CEO Mike Ullman and it's unclear what he will do now. However, she sees a low chance that he unloads his 17 percent stake.
"If he remains a shareholder, we believe he could try to drum up support from fellow shareholders and potentially wage a proxy fight,"she wrote. "Second, when does JCP hire a new CEO? We think around year-end and believe Ullman should stay on in some capacity (similar to the original plan with Ron Johnson to ensure a smooth transition)."
She noted it was a positive that former Federated Dept.Store director and executive Ronald Tysoe was named to the board. Federated is now Macy's.
—By CNBC's Patti Domm. Follow here on Twitter @pattidomm.