It depends on the type of startup. If your business sales directly to customers (e.g. b2b enterprise software) and if your business needs to partner with some manufacturers/service providers - then the 'networking' skill is important.
It is also important for doing Customer Development, but I tend not to overestimate it. It's certainly good to 'get out of the building' to speak to the customers, but if you are planning to sell your product/service through the web site, you have to design and build your sales channel with 'automated' sales in mind from the very beginning, and face-to-face meetings probably will not help in that case.