Best beginner resources for understanding the EAV database model? [closed]

I'm doing some custom work with Magento, which has a database design based upon the EAV model, and I need some good resources/tutorials that explain the EAV database model. Please don't provide Wikipedia as a resource... I'm looking for something that teaches EAV in a friendly way for beginners.

Here you go. An illustrative story: http://www.simple-talk.com/opinion/opinion-pieces/bad-carma/

The friendliest thing you can do for a beginner is to teach them the down side of EAV.

The up side of EAV is so seductive that a lot of newbies will dig a very big hole for themselves before they realize it.

Hopefully the google search will reveal at least some of the down side.

In a nutshell, EAV is optimized for getting data in, not getting data out. But that might be an acceptable trade-off. I managed a project that had to develop a general clinical trial data management system. There could not be many common data elements because each trial needs to collect different data. Capturing data was urgent; we had to develop data entry pages under pressure. Reports are harder with EAV, but they're also less urgent, and with some clever thought they can be simplified a bit. EAV has served us well.