I think we’ve seen both trends you mention, though personally I’ve seen consumerization changing IT for some time. I remember in the early 90s AOL and personal email started to catch on, which forced IT’s hand into providing work email and internet, albeit with limitations. A few years later, once we’d become accustomed to using AIM in our personal lives, it became a staple in the corporate world, though many organizations limited it to employee-to-employee communication, without access to the outside.
Now, with the proliferation of iPhones, Androids, iPads, etc. throughout the enterprise, I think these consumer-driven initiatives point to the inevitability of consumerization of IT. New technology always will find its way from consumer use to the enterprise, assuming it can be applied for business value. As you noted, organizations now struggle with the balance between giving users access to these new technologies and protecting and managing the enterprise.
In my opinion, it’s not if bring your own device (BYOD) and other consumerization initiatives are going to happen – it’s a matter of when. I wrote a blog post on this topic; please feel free to read and let me know what you think: [A href="http://blog.matrix42.com/content/consumerization-it-nothing-new"]http://blog.matrix42.com/content/consumerization-it-nothing-new[/A].