I use it so often that I have it bound to a Quicksilver hotkey. I must use it at least 5 times a day.
Even in the cases where the layout isn't particularly bad the consistency of reading things formatted in a way you're used to makes stuff easier to read.
Until today I always used to CTRL+Scroll and highlight text... NO MORE :)
I have it on my FF bar now... would love the feature to change the style it while looking at the page.. different pages need different reading styles for me.
Would like to be able to change settings once the page has been loaded though.