Do you have any button symbols or web objects on a Master page? I've found that button symbols on a master page really slow things down. Try moving them to a shared layer on a child page instead.
I use a couple of symbols, but they are literally rounded rectangle boxes with the 9 way slice to preserve the corner radius when I resize.
I've just created them as symbols and then use them on multiple pages. I don't use shared layers or master pages at all.
I've now upgraded my MBP to a SSD drive and the machine in general flies (opening Aperture down from 26 secs to just 3 secs) and I've installed the trial of Fireworks CS6.
The problem is still there. Take a 36mb file using no symbols, move an item hit save and it still taking 10-12 seconds. So there its nothing to do hardware - Its a real shame as Fireworks is close to be the ideal product but this major flaw makes it almost unusable in busy day to day environment