On the off chance that you might have missed it, I am not a huge fan of spending a lot of time on design. Unless you are trying to market your great design skills, of course. 
That said, I will agree that the default WordPress theme (or any other script’s default theme) is boring. Sooner or later, I will change this theme. Maybe. It is still low on the priorities.
As of this moment, you will notice that I still have the default theme on this blog and on the other blogs on this domain that I personally run. The reason is because it really does not matter much.
As a visitor, you are here to see the content, not the presentation.
Does the site work? Is the content easy to navigate? Do all the usability needs get met? Is the advertising (if applicable) in the right spot(s)? Is your SEO in place and being worked? Is the content worth the visitor’s time? These are the important things (in no particular order) that you need to address with any site.
Don’t get me wrong, a FUGLY site is bad! But with blogs, there are themes to start with. Pick one and run with it.
