Marissa Mayer Yahoo CEOWall Street seems to be largely unimpressed by last night’s announcement that former Google exec Marissa Mayer signed on to be Yahoo‘s fifth CEO in five years. The Internet company’s shares beat a quick retreat following a +1.3% open the morning. They’re now down more than 1% as investors await Yahoo’s Q2 earnings report after the market closes this afternoon. Several analysts say they’re taking a wait-and-see view of Mayer. Her background as an engineer “will give her credibility among Yahoo!’s staff and help her to focus the company’s efforts on creating new and innovative products,” says Barclays Equity Research’s Anthony DiClemente. But she has no experience running ad-based media content operations, which remain Yahoo’s “greatest assets for driving traffic.” And, unlike Google, “Yahoo! is a turn-around story,” says Bernstein Research’s Carlos Kirjner. “It is certainly not a rocket ship. Some will contend it is a sinking ship. It remains to be seen whether she can be an effective leader of a turn-around.” Mayer has a lot on her mind: She told Fortune magazine last night that she’s pregnant, with a boy due in early October. “My maternity leave will be a few weeks long and I’ll work throughout it,” she said.