McDonald's president and COO Ralph Alvarez says in this article on Reuters that the trans-fat-free oil that Wendy's is using does not work well for McDonald's fries.

I'm not sure why that is the case, but then I don't know the particulars. Maybe the coating on McD's fries interferes, or the taste changes radically. At an rate, I wonder why a powerhouse like McDonald's can't force the R&D on this and make it happen. After all, twenty-five-unit Pat & Oscar's did it, and I hear casual dining chains like Cheesecake Factory have found solutions, too.

For more on the trans fats issue, listen to the latest QSK Podcast, or read this or this.

UPDATE: Meant to ask: Has anyone tried Wendy's since the first of September? Can you taste (or feel) any difference in the fries or other fried items? I'm dying to know! We haven't gone yet. Click on Comment and let me know.