ive used Eusing Free Registry Cleaner for my registry and noticed a difference the first time i used it. ive used it many times and suffered no problems because of it. just adding on to what has been said =)
i would also like to add to 7. Applications Autorunning on Startup. theres a website i like to visit to check what a program or enty in the starup does to decided whether or not to disable it. it tells you what the entry is, does, and if its nessisary, optional, or not required/malware/virus/worm
http://www.ypl.info/startups/startups_all.htm