Unfortunately, it's a bad habit that 90%+ of your potential user/customer base has. People are only going to spend about 30 seconds or so on average looking at the main page before deciding whether it's worthwhile to their current objective to continue on your site, therefore initial impressions are important.
I understand that, what I mean is that people are judging on the look cause I am using twitter bootstrap, I have about ~5 sites that use twitter bootstrap and the user growth is the same as the site I created and hired a designer so I don't see how twitter bootstrap tells people that my site isn't "worthwhile" there current objective.