Recently, the graphic designers I work with have moved toward Adobe Illustrator (in pixel preview mode) for prototyping, since Illustrator is an app they already know and love. Sadly, for site builders, it doesn't hold a candle to Fireworks.
Like its cousin Dreamweaver, the Fireworks CS4 beta is girthy, at 759MB. Who knows what fraction of that is test code, or how lean it will get upon final release? Nevertheless, it doesn't feel any faster or slower than previous versions of Fireworks, but this is on a reasonably-new Intel iMac. This might lead some to cry "bloatware." I don't disagree.
Long-time users of Fireworks will be either relieved or angered by the fact that CS4 is more-or-less the same. There are a few feature additions that could make this update worthwhile, but that depends on how much you use Fireworks in your workflow.
The new user interface -- if it's typical of all the CS4 apps -- will upset a lot of people. Not that Adobe ever really followed Apple's human interface guidelines, but this departure is pretty substantial. By default, Fireworks includes tools in (what would normally be) the app's title bar. The tools are also located in the tool palette, of course, but strangely have different icons. And, so far, the Fireworks icon does nothing when you click on it.
Strangely, Dreamweaver's beta interface isn't consistent with this one.
I was all ready to hate it, but using the interface is ... well ... not bad. Having all the palettes and UI contained within one monolithic workspace is kind of nice. Even so, you can turn off the "application frame" in the Window menu, and everything is back to normal. You can even drag tabs from different windows into one window, which is a nice touch. Fireworks windows do retain, however, the custom widgets (that don't show the dot in the close button if the file has been edited) no matter which window mode you choose.
In a small nomenclature change, "frames" are now called "states," for those of you building animated images, or using rollover behaviors.
For rapid prototyping, the new export functions are impressive. Exporting to "CSS and Images" produces a layout that works pretty well with minimum effort, and validates to boot. If you need to create a live website comp to show a client (and quick!), this is a great way to do it.
Capitalizing on support for pages added in CS3, Fireworks CS4 adds PDF export to its feature list. You can set slices to link to other pages in your file, and then use the exported PDF as if it were a "live" website living within Acrobat or Preview. This is a boon for designers who haven't engaged their coding crew yet, but want to show a functioning prototype.
Now, the most disappointing thing for me is what hasn't changed. There are things that have frustrated me about Fireworks for some time that are still present in CS4. Mostly these have to do with analogous features in Photoshop or Illustrator, which could be easier than ever for Adobe to integrate.
First, Fireworks still edits bitmaps destructively. For an example of what I mean, place a photo in Fireworks, scale it down, and scale it back up. Fireworks discards the extra image data during the downsampling process. Photoshop accomplished this (though in reverse, with vector data) using "smart objects." Fireworks would do well to take a page out of Photoshop's book here.
Second, text handling in Fireworks lags far behind. Fireworks still uses a drop-down control for font selection (like Flash, but unlike Photoshop and Illustrator) which makes selecting fonts a slow hassle if you have many installed. Photoshop (and Illustrator) key combinations for changing line spacing and font size are absent (And yes, I set the keyboard shortcuts to "Photoshop"). Operations on large blocks of text are painfully slow: Increasing the letterspacing on a three-paragraph block of text locked up the app for a good two minutes.
Third, image optimization still uses the Fireworks engine, instead of the ImageReady engine that Photoshop and Illustrator use. I don't have a particular favorite among the two, but using the same one to at least ensure consistent results could be a good idea. That said, rebuilding the color palette on an optimized GIF image is still pretty quirky in Fireworks.
You might be saying, "with these changes, we might as well be using Photoshop to do rapid prototyping!" This may be true, but the way Fireworks handles objects in the layout is fundamentally different than Photoshop (perhaps closer to Illustrator), and in my opinion, better for prototyping. It's a strange middle-ground between Photoshop and Illustrator: layouts are restricted to a certain pixel size and density, but have lots of non-bitmap objects.
Hopefully, though, Fireworks CS4 continues its path to improvement, and will hold its own next to the less-apt Photoshop and Illustrator for site prototyping.