Any ideas why everything is running poorly?

Question

Hi, everyone. I have an i5 Mac Mini (2.5 GHz, 8 GB RAM. Currently running 10.7 but can go to 10.8 when the urge overtakes me.) that had been running great until about two weeks ago. My mouse (Steelseries Ultimate WoW mouse) suddenly started behaving erratically if I leave the system idle for a long period of time. The cursor would jump all over the place, wouldn't respond to clicks, etc. I reinstalled the drivers... no dice. Switched for a different mouse (generic Logitech USB), same problem. Tried disabling the screen saver and system sleep options - since it usually seemed to happen after those came up - and still no fix
My keyboard (Razer BlackWidow Ultimate) then started "doubling" key inputs, or not responding to them. Again, reinstalled drivers, nothing. Tried my old Apple keyboard, same issues. Tried switching which USB ports, both on and off my hub, they're plugged in to. Unhelpful.
I ran a virus/malware check. Found a couple of pfishers in e-mails I hadn't opened, removed them, but that was all. Problem continued.
Then Pages and my games (primarily Left 4 Dead, Binding of Isaac, Witcher 2 and Diablo 3) began behaving extremely erratically. Sometimes they'd run fine as they always had, then they'd run terribly slowly and jerkily. Turned them to their minimum settings, problems continued. L4D and Isaac are being run through Steam, if that matters. Witcher I've got both the Steam download and the Apple Store download, both versions experience the issue. Diablo behaves the worst of all.
Virus/malware scan again. Three different brands. Nothing found.
Did the internet reboot (Holding R when restarting), reformatted and zeroed the hard drive, reinstalled (at this point it forced me back to 10.7... I had previously been running 10.8). Redownloaded all the assorted drivers, redownloaded all the virus scan software, reinstalled Steam, Pages, Diablo and Chrome. Have done NOTHING else to it. Still reporting no problems. Still running badly with random key doubling and mouse being spastic with the added entertainment of Netflix and Facebook crashing every other time I open them or running like molasses when they do decide to load. Ran Disk Utility, Verified Disk and Permissions. No problems on the disk itself, one tweaked Permission that I then repaired. Still no fix. Loaded the System Monitor, checked My Processes, Idle Processes and All Processes, nothing out of the ordinary in terms of either computer/memory usage or names that shouldn't be there so far as I could tell.
I've run out of ideas and this is growing steadily more aggravating. Help! XD Thanks.

Answer 1

Please read this whole message before doing anything.
This procedure is a diagnostic test. It’s unlikely to solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.
The purpose of the test is to determine whether your problem is caused by third-party system modifications that load automatically at startup or login. 
Disconnect all wired peripherals except those needed for the test, and remove all aftermarket expansion cards. Boot in safe mode* and log in to the account with the problem. The instructions provided by Apple are as follows:
Shut down your computer, wait 30 seconds, and then hold down the shift key while pressing the power button.
When you see the gray Apple logo, release the shift key.
If you are prompted to log in, type your password, and then hold down the shift key again as you click  Log in.
*Note: If FileVault is enabled under OS X 10.7 or later, or if a firmware password is set, or if the boot volume is a software RAID, you can’t boot in safe mode. Safe mode is much slower to boot and run than normal, and some things won’t work at all, including wireless networking on certain Macs.  The next normal boot may also be somewhat slow.
The login screen appears even if you usually log in automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin. Test while in safe mode. Same problem? After testing, reboot as usual (i.e., not in safe mode) and verify that you still have the problem. Post the results of the test.