Adobe Fireworks

Yes it is used, we've been using it for years. It's great for complex work - pages, master pages, symbols, vector+bitmap in one, multipage PNGs are all very helpful. Objects are much faster to manipulate, especially mass manipulate, than layers. I think that Google use FW in their design work, as far as I remember from their job postings.

In recent years design has moved away from heavily textured 3D designs to be cut up in their entirety towards more object oriented, light and CSS driven layouts so FW is great for this type of work (note recent CSS3 export panel for FW CS5 - symptomatic). Photoshop cannot be beaten when it comes to brushes, rich textures, retouching and advanced color correction work but for web layouts, apps and mobile layouts FW is quite fantastic.

Short answer: YES you should use Fireworks.

Longer answer with reasons for using FIREWORKS and not PHOTOSHOP when creating on-screen graphics:

FILTERS
PS: Adding a blur to a shape, you have to rasterize it.
FW: You can add any filter to any object

PS: Suddenly you can't use a certain filter for a certain layer. There are no explanations on why this is the case and you can't even see the fly-out menu with filters that "used to be there".
FW: You can apply anything to anything at any time

VECTORS
PS: Shape layers are more confusing than they have to be. You can't apply effects to vectors in Photoshop.
FW: You can interact with vectors directly in the artwork, just click on it and you can move it around without having to pay close attention to which layer the object is on.

OBJECT PROPERTIES
PS: Rounded rectangles: You can't change the radius after drawing it. You can't see the result of the radius until you have drawn it.
FW: Each object can be reviewed and analyzed quickly by looking at the property inspector when the object is selected. A rectangular shape has a "rounded corner" setting and when changing the value it updates in real time.

CONTROLLING & SELECTING
PS: You can select an object from the canvas by holding down ctrl (PC) but after adding a few objects to the artwork you basically have to work from the layers if you don't want to interact with pop-up dialogues telling you layers are empty or locked etc. You basically have to name every object you create in order to find it again. Selecting something from the canvas when you get a complex document is just impossible. You end up "searching" for your objects for way to long. This makes it trickier to "sketch" or make something quickly in PS. Example: Draw ten lines on top of each other in random directions. Try moving or changing one of the lines without interacting with the layer panel. It's pretty much impossible without naming every object. The objects you draw are "sinking into the artwork" and the more you create, the harder it will be to get hold of them.
FW: Every object lights up as soon as you hoover over it, letting you know you can select it by just clicking. If you need to select an object that lies below the highlighted one there is a "select behind" tool

PIXELS
PS: Nudging a pixel when zoomed in further than 100% or less than 100% and the object will move in half-pixels (etc). There isn't even a setting to get the nudging to snap to pixels.
FW: One nudge click equals one pixel. You can set each object to be anti-aliased or not, there is even a "snap to pixel" fuction for objects that might be off-pixel, real simple (when using sub selection tool you can move anchor points to half-pixels)

LOCKING
PS: Even if a layer is locked you can accidentally select that layer.
FW: A locked layer is locked and you will not be bothered by it.

TRANSFORMATIONS
PS: When a transform is ongoing, or a text field is being altered, you can do nothing except work with the transformation. You can't close a document, you can't "unselect" by clicking on the outside, in other words you are locked until you press enter (or ctrl-enter when working with text). Because of this you have to let go of the mouse/pen and interrupt your workflow.
FW: You hold down ctrl and press outside of the object and you are ready to interact with other objects. A very quick way to work.

HIDING
PS: When you press ctrl-H it means you want to hide all the stuff around an object but when you do that for a text you still have the "transformation box" around the string.
FW: Ctrl-H hides everything and you can see the artwork clearly.

MULTIPLE OBJECTS
PS: If you want to apply a layer blend mode for more than one object you have to do it one object at a time. When selecting two at the same time, PS "forgets" what modes they have. Even if they have the same mode.
FW: You can select multiple objects on multiple layers and create the same blend modes for them. You can add the same effects to them etc. Even if they have different properties before.

COLORS
PS: When selecting a color for an object or a shape you might want to select other colors than the ones in the artwork, say for instance the color of a shape in the layer panel. You can't.
FW: You can sample colors from anywhere on the screen, even from the FW GUI if you would like to.

GRADIENTS
PS: Handling gradients is cumbersome.
FW: Every vector object can be set to have "Gradient fill" instead of "Solid fill" in the property inspector. The gradient is then controlled from either the property inspector or the actual object. Like in Illustrator but in a more straight forward way.

- - -

Other benefits with FIREWORKS:
- PAGES. Great (and fast) way of organizing your work.
- QUICK PROTOTYPING with linking and toolboxes filled with functional UI elements
- SYMBOLS. Well developed in FW. Compared to PS and AI the handling of symbols (smart objects) is superior.
- PROPERTY INSPECTOR. Instead of showing effects etc in the layer panel you see and alter the effects by clicking on the object.

This list is just recently started will get longer with time.