Also the contrast between the description text, button text etc and their backgrounds is way too low.
It feels really stripy, you could probably remove some of the horizontal lines and let it flow a bit more.
I thought the "tweetmeme.com", "reddit.com" descriptors were buttons but apparently they aren't. They look like they are.
I agree with all your points, I'll see what I can come up with.
By the way, are you suggesting me to loose the horizontal lines separating the articles?
yes, separating the articles and in the sidebar. You could consider it. I personally find a horizontal line breaks vertical reading/scanning flow, and people generally overuse the technique to separate sections where a heading in slightly larger/bolder font and a bit of white space is much more pleasant. I'm not a visual designer, just my personal preference. Up to you.