From the experiences of people I know, it helps if your startup is either capital-intensive (think building a chip) or is solving a really hard technical problem (think Google, DNA sequencing, or auto-parallelizing compilers). In those cases, the fact that you ostensibly advanced human knowledge in some small way serves as a predictor that you might be able to do it again, which inspires confidence. If your startup doesn't fall into either category -- and most don't -- it's less helpful.