For me it's clear.
Unless devs want user backlash, they need to listen.
Commonly they choose business motivation over engagement of their core users. It
Kills the site, every time.

Sloppy coding habits, excess reliance on javascript and other
Lame technologies like Flash, not to mention ugly banner
Advertisements can lead to total
Suckage if they're abused. LinuxToday was another great site before some
Ham-fisted attempts to bring in more revenue led to more ads than articles and the
Death of the community that so
Often had interesting conversations on
That site.

Before you start making a site flashy you've got to get the basics right.
Even relatively complex things can be done simply, and if you choose flash over substance
The readers that have an
Alternative will flee your sucky site like rats abandoning a sinking ship.