Just get it out there and watch carefully how people use it. In the early days of thin traffic I read the raw logs but before long use web analytics.
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.