How come, ever since I installed Mountain Lion, my computer is slower???

Question

How come, ever since I installed Mountain Lion, my computer is slower???

Answer 1

First, back up all data immediately, as your boot drive may be failing.
Launch the usual set of applications you use when you notice the problem.
Step 1
Launch the Activity Monitor application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Activity Monitor in the page that opens.
Select the CPU tab of the Activity Monitor window.
Select All Processes from the menu in the toolbar, if not already selected.
Click the heading of the % CPU column in the process table to sort the entries by CPU usage. You may have to click it twice to get the highest value at the top. What is it, and what is the process? Also post the values for % User, % System, and % Idle at the bottom of the window.
Select the System Memory tab. What values are shown in the bottom part of the window for Page outs and Swap used?
Next, select the Disk Activity tab. What approximate values are shown for Reads in/sec and Writes out/sec?
Step 2
You must be logged in as an administrator to carry out this step.
Launch the Console application in the same way as above. Make sure the title of the Console window is All Messages. If it isn't, select All Messages from the SYSTEM LOG QUERIES menu on the left.
Post the 50 or so most recent messages in the log — the text, please, not a screenshot.
Important: Some personal information, such as your name, may appear in the log. Edit it out before posting.