I tried using eAccelerator alone and then integrated it with PHP Zend Optimizer for better performance. The result was surprising.

eAccelerator alone came up slightly ahead in several tests and was at least equal in performance to eAccelerator with Zend Optimizer combined, even with further optimization to Zend default setup.

I used eAccelerator with 128 MB RAM ( eaccelerator.shm_size = "128″ ). My average idle time of CPU moved up from 50% to 82%, measured over 36 hours. As a result this site should be more responsive now. Let me know if you face any site unavailable problems by emailing me angsuman at taragana dot com.

I realized the biggest culprit contributing to CPU load is spam comment bots. I am working to devise a solution to stop them earlier in their tracks and further reduce the load.

Three minor irritants:
1. eAccelerator control panel buttons apparently do not work.
2. I was unable to disable the control panel even after recompiling without the info option
3. The default configuration needs to be changed to enable extension= line by default instead of the zend_extension line (current default).

Notes: You can find whether it is really working is by enabling the log file and tail -f'ing the log. You will be amazed. It also helped me to debug the problem where the cache file wasn't being created because /tmp/eaccelerator directory needed to be created and chowned to apache.
However do remember to turn off logging after you are done.

The bottomline is that I strongly recommend eAccelerator for any dedicated hosting users and even for VPS users to reduce CPU load and improve performance. It gives you an extra ounce of speed even from badly written php scripts. I noticed improvements across the board.