Overall, the design isn't bad, but there are a number of issues in my opinion:
1. The 'Popular Posts' area doesn't look too good, although the placement is great considering that's where visitors eyes always end up when first visiting. It just needs spucing up a little, at the moment it just looks like it's placed there to full a gap in the header.
2. I feel that the RRS box doesn't work, the colour is fine, but the size isn't. I feel that it should be the same width as the right side column as it throws off the flow of the website as it is at the moment. With that resized, you could then move over the 'Popular Posts' section to the right a little so it's inline with the right hand side column of posts.
3. 'Blogging Categories' - Not really sure why it's there? I don't like it there personal, but others might so this is more personal taste than anything. I believe the categories module belongs in the column as I shouldn't need to look for it, it should just be there, where it always is (most of the time). But if you do keep it there, add a nice gradient to the background, and maybe some bullet points.
Other than the issues listed, and I can't see any other serious things that need mentioning.
The colour scheme is great, good choice of fonts on the all the headers, the link colours are perfect, and so on.