This does two things:
1. It obscures the actual title of the post. Many feed readers are loaded in the sidebar, which has a limited width. You should be making the best use of this space.
2. It makes it harder to scan the items to find something of interest. I can’t scan the first few words of each title, since each title actually begins at a different point for each item, depending on the length of the category name. I’ve found that I rarely read items from the Gizmodo feed just because it’s difficult to parse the titles for interesting news, but I read Engadget much more frequently for the opposite reason.
As far as I am concerned, these prologues add no value. Gawker: please either use the <category> tag in RSS for this information or provide a feed that doesn’t have it at all.