You're either engineering, design or marketing, and preferably more than one.
My background is in engineering, which means I didn't have much need to pick up design, marketing, or entrepreneurial/business skills while growing up. Once I realized I wanted to work for startups (about a decade before founding my first startup) I started learning about these things. Design, as in graphic design, is probably the hardest to teach. Business is the easiest.
If your background is you got a BS in "Business" or an MBA and you want to be in startups, then you should figure out what role you're going to play. (And it shouldn't be "CEO".) Pick up some engineering, design or marketing.
Show me someone who designed and marketed several extremely popular websites when they were in college, say, along with a technical buddy who made them, and I'll see someone who can greatly benefit a startup (whether their degree is an MBA or a BS in art appreciation.)
Eventually if your startup gets big enough, or for some business models (eg: Groupon) you may need large numbers of sales guys or "Bizdev". Well, "BizDev" is just sales to other businesses where you sell a partnership. Sales guys sink or swim on bringing in business, and I think nothing will kill the "whartonite" sense of entitlement more than working on a commission.
Much respect to sales guys, though. I have done that job because I knew I'd never be able to hire a sales force if I hadn't ever done the job. It is not easy.
So, Engineering, Design, Marketing. Which hat do you wear?