I have checked your website in Chrome, Firefox, Safari and IE and the only browser I found this happening is IE. That’s probably because IE’s font antialiasing makes text look wider.
Since you’re not using menu item descriptions try switching to the small navbar under Theme Options → General → Navbar Size, this will decrease the padding on menu items and allow for more space between the site title and navigation.
If you still want to use the large navbar you can decrease the padding on menu items by adding this to your custom CSS:
.navbar-large .nav > li > a {
padding-left: 15px;
padding-right: 15px;
}
By the way, I like what you did with your website, this is one of the few occasions I see the theme’s features put to proper use. I have one small observation: I see you wanted to remove the blog tagline by deleting the text from “Blog Pages Header Text”, this however left a horizontal line above the blog posts. The proper way to remove the tagline is to go to Theme Options → Templates and drag the “Archive Location” function from the right to the left column.