In an article on Web 2.0 adoption, Ann All cites a few pieces of evidence that Web 2.0 adoption is slowing or even falling into disfavor:

In my post about a slowdown in IT hiring, I cited an InfoWorld item that quotes M. Victor Janulaitis, CEO at IT staffing research company Janco Associates, as saying that the sluggish economy has halted Web 2.0 investments. Demand for Web 2.0 technologies has “atrophied,” says Janulaitis, after “a slight increase in demand” earlier this year.
Indeed, Web 2.0 deployments likely fall under the discretionary spending column at most companies, and thus are prone to elimination as tech execs look to cut IT spending. As a Goldman Sachs analyst put it, execs are “searching for solutions with a high and fast ROI,” a criteria mostly lacking in Web 2.0 technologies.

Ann also writes:

But check out the Robert Half numbers of CIOs taking a pass on technologies: tagging software (67 percent), blogs (72 percent),wikis (74 percent) and virtual worlds (84 percent). ZDNet’s Dignan expresses surprise at the lack of love for wikis and speculates that maybe they are popular among in-the-trenches types such as software developers and project managers but not among CIOs.

I think that Ann and the sources she quotes are missing the elephant in the room: employees are adopting these technologies whether the CIO wants them to or not. Professional blogs and professional social networking tools are still on the rise, and don’t depend on internal IT resources. Likewise, wikis and community tools are available from hosted providers, usually for free. All it takes is one enterprising person from marketing to start a customer community, or an enterprising developer to start a wiki. 

When social media tools are hosted internally, I’ve witnessed over and over that they start as skunk works projects, below the radar of official IT. So the CIO may not endorse Web 2.0 tools, but company employees will adopting them both inside and outside the company firewall. In fact, the biggest risk that a CIO may cause by not adopting Web 2.0 technology in an appropriate and timely fashion is the exodus of implicit and explicit company confidential information outside the firewall.
And regardless of what the company may officially do, and what employees may unofficially do, of course a company’s customers can and will adopt Web 2.0 technology on their own.