You haven't really given us enough information to answer your question. In fact, I suspect you haven't yet asked the question(s) you really want/need to ask. I think you need to spend some time getting familiar with the top most popular F/OSS licenses, and the implications of each of them. There's a really good book on that very topic titled
Understanding Open Source and Free Software Licensing. I recommend you read it for a good introduction:
http://oreilly.com/catalog/osfreesoft/book/
For example, is building a social network or designing a template using a GPL software package a bad business plan?
Using, or not using, F/OSS isn't a business plan, it's just a detail - one element of many in a business model/plan. Whether or not it's a bad idea would depend on the other elements of said model. That said, Red Hat and others have proven the validity of selling F/OSS, if that's what you're getting at.