I've been looking into upgrading the forum to vBulletin 5. I've gained enough in advertising to purchase some of the plugins we use which will assist in the transition of some of the data to the upgraded version.
What that means is that your rep should stay the same and you should still retain your like/dislike history. The only real issue is with the feedback in the classifieds, but it's used so infrequently that losing that data will not really be felt. Most of the work has been research at this point. Once I have everything sorted out, I'll run some upgrade tests on the dev system and work out the kinks and make sure the upgrade is as smooth as can be.
I've put off the upgrade for a while as there was no real benefit to doing it. With some of the issues that have cropped up in the text editor and the aging codebase in vB4, it's getting to the point that it's necessary to upgrade. There is also no feature development being done on vB4: there are only bug and security fixes. vB5 should take more advantage of modern browsers.
The forum WILL look different The way you use the forum will change. It may be scary and uncomfortable, but I'm sure you guys will be able to work through it.
I've been doing this in the little free time I've had as I've got a couple of high-effort projects going on at work, so it's not going to happen super fast. By the time I get all my ducks in a row, I should be able to give a useful time estimate on how long the forum will be unavailable during the upgrade. That means I'll also try to give y'all a 24-72 hour heads up on the outage.