The most thing I don't like of skype chat style is the waste of space. Luckily there is a way to change it. It's very easy, because it's just css -- just like a little bit of Webdesign, what is part of my daily job as a Drupal specialist.
It's almost the same as Skype 5.1 Chat style. But the old Skype 6 chat styles are not working anymore due to some changes. Eg. did you notice the new chat icons? Anyway, the new Skype 6 theme isn't better than the styles before. So I just modified the new Panamericana.SkypeChatStyle from Skype 6.0 and added my modifications from Skype 5.1. to minimize the waste of space.
Here is a step by step tutorial how you can modify the Skype chat theme:
Copy the recources from /Applications/Skype.app/Contents/Resources/ChatStyles/Panamericana.SkypeChatStyle to ~/Library/Application\ Support/Skype/ChatStyles (create the folder if it doesn't exist).
Edit the Info.plist to set the name of your style.
Modify the main.css inside the package (right click Show Package Contents >> Contents/Resources/css/).
Restart Skype and go to preferences and change the messaging style. That's it.
If you just want the original Panamericana style to occupy less space, you may download and unzip my version and place it under: ~/Library/Application\ Support/Skype/ChatStyles