2011 MacBook Pro running very slow since OS X 10.8

"I've taken my MBP into the Apple stores numerous times over the last ten months, and the hard drive & the mother board has been replaced, but I still have the same frustrating keystroke lagging & text / data entry software freezing."

What size is this MBP? There's a recall in the larger models:

Apple Recall

https://www.apple.com/support/macbookpro-videoissues/

" the hard drive & the mother board has been replaced,"

If yours qualifies then you would be reimbursed the cost of this if it wasn't done under AppleCare.

Go here:

Etrecheck

http://www.etresoft.com/etrecheck

and download Etrecheck, run it and post the results here.

"I only fill my hard drive to 90% of it's capacity at most."

This article is pretty old but still the infor is pretty much standard thinking:

"The first landmark isn't one that will necessarily trigger any alerts, and occurs when your drive nears 90% of its capacity. Your Mac needs at least 10% free space on the drive to help it keep files in a neat, contiguous order (a process known as defragmentation).

As your drive fills up and the defrag process grinds to a halt, your files start to get split up into multiple parts to fit the available space, ending up physically scattered all over your drive.

File fragmentation may not be an issue for newer solid-state drives (SSDs) due to their lack of moving parts and an ability to access any part of the drive almost instantaneously. But for the vast majority with traditional drives (HDDs) which utilise rotating platters and mechanical drive arms, fragmentation is the first tell-tale sign that all is not well."

You could also consider installing an SSD.

There's a reason that Apple has been putting SSDs in the MBAirs from the very beginning.

When you see a beachball cursor or the slowness is especially bad, note the exact time: hour, minute, second.

These instructions must be carried out as an administrator. If you have only one user account, you are the administrator.

Launch the Console 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 and start typing the name.

The title of the Console window should be All Messages. If it isn't, select

SYSTEM LOG QUERIES ▹ All Messages

from the log list on the left. If you don't see that list, select

View ▹ Show Log List

from the menu bar at the top of the screen.

Each message in the log begins with the date and time when it was entered. Scroll back to the time you noted above.

Select the messages entered from then until the end of the episode, or until they start to repeat, whichever comes first.

Copy the messages to the Clipboard by pressing the key combination command-C. Paste into a reply to this message by pressing command-V.

The log contains a vast amount of information, almost all of it useless for solving any particular problem. When posting a log extract, be selective. A few dozen lines are almost always more than enough.

Please don't indiscriminately dump thousands of lines from the log into this discussion.

Please don't post screenshots of log messages—post the text.

Some private information, such as your name, may appear in the log. Anonymize before posting.

When you post the log extract, you might see an error message on the web page: "You have included content in your post that is not permitted," or "The message contains invalid characters." That's a bug in the forum software. Please post the text on Pastebin, then post a link here to the page you created.