Bootstrapping is always preferable... if possible.
Unfortunately, one of the most common causes of failure in new business ventures is a lack of capital.
You need to be very realistic if bootstrapping a new venture will allow you to survive through the startup phase and into a period of growth.
Many estimate that you should have capital equal to about three months of expenses before starting a new venture. I personally believe this is not enough.
When starting a new business, your focus will be drawn in many different directions, most of which you won't be able to anticipate before you begin. Expenses are sure to exceed your early expectations. Dealing with not having enough funds to run your business makes success a long-shot.
If you run out of personal funds and are depending on your customers exclusively to fund your business, the additional pressure you'll feel and ultimately place on your customers can be a killer to your new venture.