Take a look at what happened to this blog’s hit counts after switching (briefly) to a new and free WordPress theme downloaded from the official WordPress website.
Before I used my own variation of the freely available sandbox theme. I switched after updating the template andlosing some of my work on it. Now I’ve gone back with though I haven’t put any real effort into making the site look “good.”
Since replacing the theme, my site’s stats have returned to normal. I won’t name the theme that killed my blog’s stats for about a week, because that’s mean, but it should serve as a warning. By itself the sandbox theme is fairly SEO friendly, but with with a little tinkering you can get something that knocks the mittens off kittens. Sandbox is the exception though, not the rule. Many of the themes available out there a garbage. It is better to make your own or pay someone with brains to do it for you.
Remember, free is sometimes good, but not always.