http://www.telegraph.co.uk/technology/6125914/How-20-popular...
OP : Thanks for asking this question. I've been pondering it last night since I am in a similar situation. Just my two cents, I've decided to use Themes from Themeforest that leverage other established frameworks (I prefer the ones that build on twitter bootstrap).
I feel like sticking to a well accepted framework allows you to benefit from further releases since bugs keep getting fixed and you can freely upgrade using the new releases without having to wait for the original author of the theme to do it for you.
I'm using an Admin template for a web app and its pretty unique.
I just don't want to be "mocked" because I didn't take the time and money to make a more unique interface. Like North Korea was mocked because the Democratic People’s Republic of Korea's site (http://korea-dpr.com) cost $15 because they bought a template of Themeforest.
I know it shouldn't be a really big problem, but I'm second guessing every decision I've made because I'm really nervous about this one. (I've switched between PHP and Python and Linode and Heroku about 15 times now).
Forget the web design stuff. Use Themeforest, or the Boostrap defaults, and spend your time getting your product to do things people will pay money for.
What does that even mean, really? Break it down.
Do you think customers will not buy if you use a ThemeForest theme or Twitter bootstrap or WooThemes or what have you? If so, empirically denied: I've sold hundreds of thousands of dollars of product on sites using those options personally, and many people have had that experience.
Do you think you owe it to the universe to hire a designer? I don't know why you'd think that, but some people apparently do, so let's time-shift that owning-designers-money thing into the future, just like designers have apparently timed-shifted giving-you-more-than-$50-for-your-programming services into the future.
Do you think "professional" sites necessarily have awesome, jawdropping unique design? That is not true and would not withstand scrutiny through the WayBack machine. The biggest Internet companies you can think of all launch withed worse than what $5 will buy you on ThemeForest. Some of them are still there (cough Craigslist).