I go through a lot of web pages and a lot of blogs and there are a few things that really irritate me in terms of usability of the site:
Open files & external links in new windows.
If I am on your site and I click on a link to a document or a link to someone else's blog, please please please open that up in another window. Most of the time, I am just clicking on a link to see what is has, then, it's a quick CTRL-W to close that window. Of course, if that was the only window, now I have lost your site.
If it "might" be clickable, it should be clickable.
If something might be clickable, just make it clickable. If you have an icon for a product, or as a section description, please make the icon clickable. If you have an "enlarge photo" link... make the photo clickable for the same action. Why make people do something intuitive and then have to figure out how else to do it.
If you have a horizontally scrolling area (ex. div or iframe), make the area a fairly small height.
I see this a lot on people's blogs. They have code examples that scroll horizontally, but their code example is sooo long that you have to scroll the page down to get to the horizontal scroll bar. Then, you have to scroll over and then scroll back up just to see the code you wanted to see originally. Don't make people do that. Just put a set height (or some other technique) that allows the user to see the horizontal and vertical scoll bars in the same browser screen.