In my case, I happen to use Opera Portable (there are also Firefox and Chrome/Iron portable apps) on an encrypted hard drive, so I neither have to worry about my browsing history, nor do I have to worry about password theft. On one level, at least.
I've checked the box for "Stay Logged In" for my profile. It's been so long since I've done this, I probably have the name wrong. "Keep me logged in"? Something like that. You won't lose your posts if you have that checked.
FWIW, vBulletin doesn't like Safari much. This is more of a problem in 4.x, but I have seen some occasional weirdness in what we use (3.x). If that fact makes you want to switch to a different browser, I'm all for it, primarily because a lot of websites don't seem to like Safari. (Standard disclaimer: I also work on Macs, I used to work for Apple, I've got a nice 27" iMac at work, I've got an older MacBook at home, etc., etc.)
The other suggestion I have is to use a word or text processing application for typing long posts. I don't do that anymore because Firefox and Opera have built-in spellcheck, but it's a good alternative. I happen to really like Notepad++.
There are a couple global settings that I haven't tweaked in awhile, but I really don't want to tweak the "auto sign off if no activity in 15 minutes" because someone might be using a computer in a library or workplace and forget to sign off. Hey, I wait for about 15 minutes to prank my coworkers that forget to log off and wander away ....