It's becoming evident that they're not really needed at all, rooted or not. Android does a pretty good job of managing memory on it's own and it keeps some programs loaded into ram for quicker start up. Killing those programs will only cause Android to replace them with others. Froyo does a pretty good job of managing memory and I've heard that Gingerbread does even better.
Your best bet is to install Titanium Backup (or do it manually by removing or renaming the files) and freeze the apps you don't need. Such as apps you've replace with others. For example, I'm running Gummy 2 and I installed Go Launcher as I like it better than ADW, so I used titanium backup to freeze ADW so it's not running at the same time.
