Are you using FW CS4? If so, have you downloaded the patch from Adobe?
I'm on a MacBook Pro and don't see any real performance issues since
applying the patch. What size files are you working with?
I'm on CS4 now but I've had the same issue with CS3 as well. The CS4 patch did fix the infamous text engine issues I was having but I haven't seen any type of performance increase.
In terms of file size, I do get pretty large but it's even this bad when I start. The test I use is to create 9 or 10 simple rectangles on a new file, give them different colors, start dragging them around the screen for a bit, and the proceed to click around. I'll immediately notice that there is a significant lag from when I click the object, and the time it takes for the properties panel to refresh. So slow that I'm able to select the color of the previous object with time to spare.
Found two more threads with the same issue...
Lag updating the properties panel
Fireworks CS4 Mac Dog slow, Lags especially with Wacom
Any macbook owners out there who are having no issues? If so, can you tell us a little about your setup?