I've been building a web application at home for a few months now and having a programmers design skills (i.e. none) means that while it works well, it doesn't look that great.
The design itself is using the standard blueprint css grid, has a top nav bar and uses the Jquery UI buttons and so on. It's not awful it's just fairly simple.
I'm getting close to the point where I want to get some trial users but I'm worried that the basic design might put some people off. You hear so many conflicting things about startups, such as "launch quickly, improve later" versus "great design sells" that I'm not sure the best course of action.
So how important is it?
When you do have an alternate design, try it side by side in an A/B test. It's very difficult to tell a "good" design by looking at it. It's pretty easy to compare and find out for certain. The biggest benefit of A/B testing is that it removes a lot of hesitation and deliberation from the development process.
Although I am a big fan of good design, it's important to note that the opinions of lots of successful people vary greatly
http://www.conversionvoodoo.com/blog/2010/04/increase-your-c...
The more you A/B test the better you will get to know your own audience and what works for your particular product.