Coding Horror talks about Robert Scoble's "irrational" desire for extreme web site portability.

Sure, I think that support for 17,000 different resolutions is a little bit nuts; but being able to have a couple of default "mobile" settings for pages might not be too out of line.  This reminds me of when I used to see "This site is optimized to work with Internet Explorer only", which in many cases really meant, "Our web designers are *really* lazy and can't be bothered making this standards-compliant". 
This isn't to say that there sometimes aren't reasons for picking IE, particularly if you are delivering a specialized web app for limited sale vs. a content site like IGN or something that will normally be seen
from many browsers.  I would say that having a non-functional website in Firefox gives a terrible impression most of the time.  Anyone remember the initial Windows Live demo?

I'm not saying that site designers who do not provide a mobile layout for their users are lazy; but I do think it is something that people should take into mind more as mobile Internet picks up speed.   Of course, many sites also do a piss-poor job of being accessible for the disabled; I wish Scoble would start carrying that torch.