My first guess is that your project is non-square pixels and you have pixel aspect ratio correction turned on in the composition panel. My second guess is that you have the composition panel set to half quality. A little more information about the project or a screenshot of your entire comp panel would be helpful.
it's a 1080p project. Pixel Aspect correction is turned off (it doesn't have any use in a 1080p project anyway). My viewer quality is "Full". The funny thing is: when I'm using the same font again and type in the same text, the text looks alright. The same goes for illustrator files that I import again. The problem is just with text layers and files that were already in the project.
If a new project looks fine when you use the same assets then there is some switch that's been thrown in your project. Make sure that all the composition settings are where they should be. Again, a screenshot of the entire project at full rez would help us catch the problem.
Another suggestion would be to start a new project, import this existing project, then open it up. That would clear all of the saved settings in the project and may reveal the problem.
I can't post a full screenshot, because it's a current european tv commercial and I don't want to post it in public. Hope you understand.
I just tried to make a new project and import the old one into it - same bug.
Anyway - I just deleted all my stuff in the project and just left one old text layer in it. I could even change the font - it still looks blocky. Then I made a new text layer with the same font and attributes and put it beneath it. You can see the difference especially in the "X".
I uploaded the small test project for you: http://www.mediafire.com/?19qik5mwfq7hbx5
When you open the project - do both text layers look correct?
Funny thing is - I never changed that switch. Same goes for my illustrator-layers. Never touched that switch anytime. Confusing.
Anyway...thank you again for your time and effort!