It entirely depends on the kind of business you have. If you have a tech startup for example, there are pretty reliable assumptions about each round of funding. And a business plan and financial forecasts are almost totally irrelevant to sophisticated tech investors in the early stages of a company's life. Recent financial history is important if the company is already generating revenue and in that case, a twelve-month projection is also meaningful, but pre-revenue, financial forecasts in tech startups mean nothing.
You shouldn't give up more than 10-15% for your first $100,000 and from that point forward, you should budget between 10-20% dilution per each round of subsequent dilution.
In a tech startup, you should be more nervous about dilution than control. The reality of it is that until at least a meaningful amount of traction is reached, no one is likely to care about taking control of the venture. If the founding team screws-up, it's likely that there will be very little energy from anyone else in trying to take-over and fix those problems.
Kevin is correct in that the board is elected by shareholders but, a board exerts a lot of influence on a company as time goes-on. So board seats shouldn't be given lightly. A single bad or ineffective board member can wreak havoc on a company, especially in the early stages of a company's life.
In companies outside of tech, you're likely going to be dealing with valuations that are far lower, thus likely to be impacted with greater dilution and also potentially far more restrictive and onerous investment terms.
If your company is a tech company, I'm happy to talk to you about the financing process. I am a startup entrepreneur who has recently raised angel and VC capital and was also formerly a VC as part of a $500,000,000 investment fund investing in every stage of tech and education companies.
