Some time ago, I did a similar thing with the CR/EL system. I noticed that there were a number of posters who had very different experiences with the system than I did. I like the CR/EL system. Stop laughing. Really I do.
Here's a few from my observation:
(1) People who interpreted the word "challenging" in the CR system to mean "memorable, life-or-death struggle". These DMs tended to be frustrated by the "broken" CR/EL system that gave them challenges which were "too easy". They responded by routinely throwing PCs against monsters 3 or 4 CRs higher than their level. This leads to an arms war syndrome: The players faced with such difficult challenges are forced to uber-optimize their characters in an effort to stay alive. The DM, convinced that all encounters should be life-and-death struggles, responds by upping the ante. Every encounter becomes a major set-piece that needs to be painstakingly designed down to the last detail because the balance between "challenging" the PCs and completely destroying them was razor-thin.
This style of play can be contrasted to the people who read "challenging" to mean "appropriate challenge that will expend some resources but is rather unlikely to prove life-threatening". Those DMs were far more willing to use EL-appropriate and even build encounters out of large numbers of lower-CR creatures. (Uber-optimizers would scoff at that type of low-CR, EL-appropriate encounters as being example of the CR/EL system being broken because the individual monsters were "too easy".)
(2) People who saw all the customization tools in 3rd Edition and decided that they needed to customize every single encounter that they ran.
This style of play can be contrasted to people who would use the customization tools only when they really needed to. For the former group, stocking a dungeon could take hours. For the latter, they could write "4 orcs" here and "2 worgs" there and be ready to roll in a couple of minutes.
(3) Allowing player control of encounter pace. Or, as Justin Alexander calls it, the Death of the Wandering Monster. This has a huge impact on how the classes perform.
(4) Similar to #3 and often resulting from #1, the "one encounter per day" standard vs. "many encounters per day".
As a particularly extreme example, in our current campaign we just wrapped up a single campaign day of activity that stretched across four gaming sessions and took up about 30 hours of table time. A lot of time was spent in character interaction and dungeon exploring, but we also wrapped up 15 combat encounters -- three of them being quite epic (one fought across multiple levels of an apartment complex; another fought against an entire platoon of enemy riflemen + spellcasters; and a third being fought through several buildings of an ancient city buried beneath the earth against more than a dozen foes). By the end of it are spellcasters were tapped out, but people just kept thinking outside of the box and trying to find new ways to contribute.