Keystrokes getting eaten randomly I have a weird problem on my 2011 MacBook Pro 15" running OS X 10.8.2. 

Every now and then - say every two days - the system starts to ignore most of the keys I press for 2-3 minutes. It's like processing of keystrokes becomes incredibly slow. If I wait for ten seconds between each key, what I type is processed completely; otherwise kys wl b msng rndomly. 

The system is not overloaded in any way when this happens. I'm usually writing something and this comes out of the blue.

Has anybody experienced the same, or could point me to some resources? I'm having a hard time coming up with a good Google query for this problem. 

It is possible this was introduced by the 10.8 upgrade but I'm not 100% sure.

I managed to run top while this occurred again and the only thing that was runnng that usually isn't is Google's ksfetch. Will post more info if I catch it again.
There can be two reasons: software or hardware.

Software

This is most likely caused by the CPU being overloaded, so the kernel is throttled. That means only number of samples that are processed for a specific period to avoid overheating to prevent the crash.

To confirm that, run the following command in Terminal:

sudo fs_usage | grep -v 0.00


which should show something like:

THROTTLED  0.015030   kernel_task
...
THROTTLED  0.019601   coreduetd
THROTTLED  0.031014   kernel_task 
...
THROTTLED  0.014947   kernel_task


which means your kernel being throttled which may result in such unexpected behaviour (see also: Why kernel may be throttled?).

I had this problem when my system was eating t letter (for all the apps) and CPU sensors (in iStat) were over 90˚

To solve the problem, check the above command fs_usage and kill unnecessary processes. If it's web browser with too many tabs and a lot of ads and JS scripts in the background, close unnecessary tabs.

There is also a chance that it's caused by I/O throughput (disk access) and your storage (e.g. SSD) may be reaching its lifespan.

Hardware

If keystrokes are eaten consistently (like the same letter over and over again), this could be physical keyboard issue.

Before blame the hardware, you should try to:


Reset NVRAM.
Reset the System Management Controller (SMC).


If that won't work, you should arrange appointment at a Genius Bar.

For temporary workaround, see: How to deal with non-working key on the keyboard?