My late 2008 MacBook Pro (2.53/4GB Ram) running Lion 10.7.3 seems to be running slower. What should I do to improve performance?

Question

My Mac feels as if it is running slower these last couple of months.  I have thought of pursuing a commercially available "clean up" product, but thought I would try the community first and also for pointers using the Mac's own internal diagnostics or system improvement capabilities.  Any and all advice is most welcome.  I have a 250GB hard drive that is half full, I always update to latest revisions and have an extra high-speed internet connection.  Computer is not heavily loaded with apps and typically using Firefox for browsing.  (MS Office for Mac as well, but usually limited to one program such as MS Word or Excel at a time.)  No heavy graphics utilization.  Videos from the internet load slowly and some are choppy.  Even scrolling just doesn't seem "brisk".
Thank you,
Tom

Answer 1

Disconnect all wired peripherals except keyboard, mouse, and monitor, if applicable. Launch the usual set of applications you use when you notice the slowdown.
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.
☞ If you’re running Mac OS X 10.7 or later, open LaunchPad. Click Utilities, then Activity Monitor in the page that opens.
Select the CPU tab. 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.
Now select the System Memory tab. What values are shown in the bottom part of the window for Page outs and Swap used?
Step 2
Launch the Console application in the same way as above, and select “kernel.log” from the file list. Post the dozen or so most recent messages in the log – the text, please, not a screenshot. If there are repeats, please post only one example of each repeated message.