ive used the iobit game booster and it does actually work but only if you have things like skype autoload when you start pc.
its a much better idea to remove startup items you wont always use.
easyist way to do this is to hold "Ctrl" and press "R"
then type "msconfig"
click "services" then "hide microsoft services"
if you see things like steam untick it. then click ok
this will stop all the programs auto loading at startup. will not stop the programs running as all the services will load when you start the programs manually
game boosters do the same sort of thing except some also do things like disable windows aero while your in a game then when you leave re-enable it this create's a small boost but its effective
yes it can crash certain programs but things like your anti-virus should be added the the programs exclusion list
http://www.iobit.com/gamebooster.html
(ive used this before and no crashes)