I have to agree with John on this one - they definitely are not a fad IMO. The fad may have been among resellers, but now I think almost all the LLL.us domains are trickling into the hands of end users and/or domainers willing to wait to find an end user. And I can also echo what John is saying about seeing more and more ads using a .us domain. It is only a matter of time before the extension takes off IMO.
Tom