Do you speak legal-ese
California, where Silicon Valley is located, is an "At-will" state. At-will means that either employer or the employee can break off the employment relationship at any time with no liability. (For exact legal applications, you should consult competent legal counsel, i.e. not me.)
Keeping your team productive
The implication for employers, especially software companies, is how to retain key employees. And, this is one of the reasons some Silicon Valley companies offer free meals, games in office, and bring-your-dog day. However, most of the "unconventional" methods are not only defensive in nature; after all, it is also true that happy employees make for a productive workforce.
One thing that is not as well appreciated in the context of at-will law is that it also makes employees more loyal. Instead of contractually tied to a position, everything else being equal, you work there because you want to.
Keep paddling
The other side of the equation is that every employees has to constantly keep up, branch out, and be flexible in applying skill sets. Stagnation is not really an option. Unlike the more established traditional industries where the success of an employee can be defined in terms of how well a long job description checklist is met, job descriptions in Silicon Valley are constantly morphing. Put another way, if there is a long laundry list of what constitutes success for a position, there is a good chance that it can be performed elsewhere at lower costs.
On a day-to-day basis, it is important to keep up with your given field. This could be getting a new technical certificatiion for an engineer or refining a business process if you are an executive. It is always a good idea to keep abreast of emerging trends so that, for example, when the CEO asks how the new distributed Hadoop database will impact company's e-commerce architecture you have a decent answer.
Finally, cross-training is the norm instead of exception in Silicon Valley because ambiguity is a given. Within a discipline, say software engineering, the transaction methods, architecture, and buseinss model requirements are ever changing. This requires the engineerings team to understand the how and why as oppose to merely "doing the work". If you need to reach across functional focuses, for example in product management - usually a marketing function but has to work closely with the engineering team - the ability to converse fluently with both users and development teams is a must.
Like Schumpeter said
As Schumpeter succinctly captured in the term "creative destruction", it is unlikely that what you do today in Silicon Valley is similar to what you did a couple of years ago. As technology, business model, and ecosystems develop, the same job title often demands vastly different skill sets within a short period of time.
For example, when Google popularized the on-line advertising model in early 2000's, there was no pre-existing pool of talents who knew exactly what to do. Initially, the closest parellels were the direct mail and mail-order catalog people. Since the transaction is done on-line, a lot of web designers also got involved. Moreover, with its ability to generate detailed quantitative data on buyers behavior, people with data analysis experiences jumped into the fray. All the while, marketing communication sand pre-sales people, who were traditionally responsible for website and generating qualified sales traffic are furiously learning and hiring new skills sets to meet a new way of doing business.
Within four to five year, by the mid-2000's, the motley crew that utilizes various aspects of the skills above has become an ecosystem known as SEO/SEM (search engine optimization/marketing) with its own tradeshow and gurus.
