I use Illustrator to rough out layouts as I find it quicker than Photoshop, and I can have several layouts and design ideas on the go in one document, but then I switch to Photoshop for finalizing the design and cutting it up.
I have a few designer friends who do all their web work in Fireworks, it remains the tool of choice for a lot of people.
I use Illustrator for all logo design and print work, unless it's a multi page document like a magazine layout, and then I move to Indesign. If I have to do Flash work I use Illustrator for that too, because I absolutely hate the drawing tools in Flash.