I have no particular interest in working in the Financial Services (Private Equity or IB or the likes) although I am deeply passionate about working in Business Development/Marketing or Strategy at predominantly tech companies. Would an MS&E get me there. Would really appreciate a reply!
From what I've seen, I'd say around 35-40% of M.S. graduates end up in finance (IB, hedge funds, PE, etc.); ~25-30% end up in consulting (Bain, BCG, Accenture, LEK...); ~20% end up in tech companies (recent ones I've heard: NVIDIA, IBM, Cisco; most are supply chain analysts); and the rest pursue other endeavours (Ph.D. programs, other degrees...)
Strangely enough, it is NOT easy to land a job in venture capital, despite the university's proximity to Sand Hill Road. Accel Partners hires only one or two each year, and last year's associate graduated from the communications department.
"Google, Facebook, LinkedIn and other valley startups. " None of the three you listed are startups, and the IPO riches are long gone (yes, even Facebook; rank-and-file employees who joined after 2009 are unlikely to become millionaires.) Join these companies now and you'll actually be compensated LOWER than the market, due to their intense media hype. At Facebook in particular, you'll also be worked to the bone (looooooong hours) and treated like a disposable worker, because applicant interest is so high that the 30-50 candidates who show up daily at Menlo Park HQ for final round interviews would each gladly donate a body part to take your position.
As for actual early-stage startups, it's not common but has been done before. If you are interested in entrepreneurship (i.e. founding your own company), you should take the 273/274/276 series of classes and join a few entrepreneurial-focused clubs/student organisations such as BASES, StartX, etc. If you are interested in working for an early-stage startup, the school holds an annual startup-focused career fair.
If you're 100% set on biz dev/strategy/marketing at a tech company, I would recommend pursuing a CS master's degree and taking the equivalent of MS&E 270 and 271 as electives. I think you'll have a much stronger resumé this way.