Anybody looking for "The Answer" has to be a bit more specific about "The Question" I suspect!
For people who want Windows, Windows CE is a clear answer to several questions. I mean, have you
compared the speed with which you can find a name or phone number in Pocket Outlook, with the tedious effort it takes under Office on an XP based PC?
And don't forget Palm. It has a tiny memory footprint compared with either Windows or CE or Linux, and places very few demands on the processor, too. The Treo 600, stupidly, doesn't have Bluetooth, otherwise I'd vote it easily into my "top smartphone" slot. (Can't be doing without hands-free when driving, sorry, Treo!).
I've got a Dana portable. It's not a PC; it has almost no graphics capabilities suitable for web browsing compared with Windows/Linux - but that can be fixed, no?
I suspect there's lots of "rwars" type debate going to occur. But there's more than just rwars to this question, too...