Firefox 3.5 and various speed tweaks?

I'm just wondering are all those speed tweaks that exist in about:config actually necessary for FF3.5?
After installing Ubuntu 9.10 a couple of weeks ago which is packaged with FF 3.5 I've noticed that FF 3.5 is significantly faster than 3.0xx. I'm not inclined to mess with it right now at least but just curious if others have "modified" the default settings in FF3.5 or left them as they are?

I used to implement some speed tweaks in Firefox but have stopped doing it because most of them didn't really seem to be worth the effort, at least in my own opinion. Firefox continues to work fast enough for me as is, but I hear some complaining that it's beginning to be too slow for them, so I don't know.