My iMac late 2009 base is starting to run a little slow, is full of folders from programmes installed and removed over the years and over the last month i have had a few issues also (scanner, printer and mouse driver issues). The system originally ran snow leopard, this was upgraded to lion and this to mountain lion. Probably going to regret saying this now i only have 1 month of applecare left but the mac has been super reliable over the last 3 years. Its left on 24/7 with only the screen set to sleep and is only restarted when needed. I use clean my mac and onyx for maintenance but I am thinking that a fresh installation of mountain Lion may help. Would be interested to hear your opinion, I have a timemachine backup, carbon copy backup and files on bluray disk but i am still nervous making the jump.