For years now, Marissa Mayer, the newly appointed Yahoo CEO was one of the most visible and well-known Google executives. She was instrumental in developing many of the services that have bested Yahoo. By hiring her, Yahoo hopes that Mayer will come up with an effective strategy to compete against the juggernaut that Google has become.

Will Mayer be able to deliver results at Yahoo the way she did at Google for last 13 years? Can hiring your competitor's employee bring success to your company? There are instances when poaching from competition resulted in a success and others where it didn't do much good on a good day and proved disastrous on a bad one. Let's look at some of these cases.

Mark Hurd: 5 Years at HP; Hired by Oracle

This can be termed as one of the most controversial stories in tech world. Last year, when Mark Hurd was forced to resign as the chairman and CEO of HP in the wake of sexual harassment charges, Oracle grasped the opportunity and hired the 55-year old as its co-president.

Right after joining Oracle, Hurd has become a controversial part of an ongoing court trial between HP and Oracle. HP sued Hurd shortly after he went to Oracle in September 2010 claiming that he violated a confidentiality provision of his severance agreement. HP also voiced concerns about Oracle attempting a hostile takeover after it hired former HP CEO Mark Hurd as co-president, Oracle's lead counsel told a judge.

This executive shift might not have been proved a major move in terms of company's growth but it definitely brought a pool of controversies for Oracle.

Pat Gelsinger: 20 Years at Intel; Hired by EMC

EMC COO Pat Gelsinger, who will be the new CEO of VMware, was an Intel executive for almost 20 years before he joined EMC in 2009. He was also the first CTO of Intel Corporation.

His efforts helped Intel in restoring its market leadership with the Xeon Products and bring out the first quad-core products to market.

He brought in new initiatives within the company during his time at EMC. He was the force behind EMC's run for Big Data. Buying NAS vendor Isilon, flash-array start-up XtremIO and integrating VFCache with VMware integration are some of the accomplishments of Gelsinger's tenure. He continues to stay as a key decision maker at EMC while heading VMware.

Gelsinger's tenure at EMC is the product of executive shift from competition and appears to be a successful move by EMC.

Meg Whitman: 13 Years at eBay; Hired by HP

As a part of its dramatic changes within the organization, HP ousted its CEO Leo Apothekar from his position less than a year after he took the job and replaced him with former eBay CEO Meg Whitman. The company justified the shake up by saying that to successfully execute its strategy, the company requires "additional attributes" in its CEO, traits that Whitman possesses.

Nevertheless, has Whitman proved her worth as a CEO yet? Unfortunately, she did not receive a beautiful legacy as CEO. A confused organization facing conflicting decisions and roadmaps charted out by previous CEOs are among the major challenges that Whitman is facing.

Former CEO Leo Apothekar was sending a message to the world when it looked as though the profitable printing and imaging division would be chopped off as HP moved more into software with the purchase of Autonomy. Whitman did an about-turn on Apothekar's game plan.

She merged IPG and PSG, reaffirmed the company's commitment to its PC business, and promised that HP's newly created Printers and Personal Systems (PPS) division will get "more than its fair share" of R&D investment in the coming years.

Whitman decided to eliminate 27,000 jobs -- about 8 percent of HP's workforce -- on the grounds that the company is sinking under its own weight and simply cannot continue at the same size. Although HP is on the verge of losing its top position in the PC market, Whitman is making all her efforts to inspire confidence and trust in the company's long-term future.

It seems one will have to wait little more to judge Whitman's work as HP CEO.

Marissa Mayer: 13 Years at Google; Hired by Yahoo

Yahoo chose Google's Marissa Mayer as its new CEO. Thirty seven-year old Mayer was Google's 20th employee and during her 13 years with the company, she was one of the most important executives at Google. Mayer had been in charge of many Google campaigns that have beleaguered Yahoo.

She is still widely considered to be among the Internet industry's brightest executives, and Yahoo is hoping that she will come up with an effective strategy to compete with Google.

Scott Thompson: 7 Years at PayPal; Hired by Yahoo

Mayer takes over from interim CEO, Ross Levinsohn, who recently replaced Scott Thompson. Prior to Yahoo, Thompson had a great time as President at the global e-commerce business company, PayPal. During his 7-year tenure at PayPal till 2012, the company's business grew significantly, which drew Yahoo towards him.

However, Thompson's charisma was not the same in Yahoo. Soon after joining Yahoo, he decided to lay off 2,000 employees, as he wanted to sweep out jobs that do not fit into his plans. This move created more controversies for the already troubled Yahoo. Ultimately, Thompson quit the company amid the controversy of fake computer science degree.

While it is too early to see the effects of Mayer's appointment, Thompson's hiring was a bitter experience for Yahoo.