My usual photo editing application and what I usually receive web layouts in is Photoshop. Since I'am working with Matt Linder and his choice of application, Fireworks, I'll will be slicing his layouts from Fireworks instead of exporting the layout to Photoshop.
The major issue I've had between Photoshop and Fireworks has been Fireworks slower responsiveness. I always feel when you select an objects in Fireworks and look at the properties palette that I am either really fast or the application takes a second to populate with its properties. That is my number one issue with the application.
Window focus is another. More often then not I usually have to click twice on an object because it seems I need to set focus to the window first before I can click on an object. This happens the most when switching between apps.
Groups, I dig this idea because I was Freehand fan but I feel this concept is a little archaic. I'm not sure if I feel this way because I'm used to Photoshop and the use of folders to group things. I don't have a huge issue with this. I think I just like my folders versus groups.
A few really positive things would be the vector capabilities and slicing techniques. It makes more sense than Photoshops slice tool but in the end I feel just these 2 things can't trump the sluggishness I get from Fireworks.