Yeah, it really is extra work.
I make my sites XHTML Transitional most of the time, and present it as text/html. I have had no issues with this at all. Maybe it's not proper. And maybe it pisses of some people, but the site works, renders exactly how I want it, and no one got hurt because of it. I see no problem there.
When I made my first XHTML site I was all happy with it (Valid XHTML strict, w00t I rock!), and then I learned about this MIME type issue, so obviously I went to see what my pages look like when they're actually treated as XHTML. One kinda noticeable difference is that my background only covered the content - not the entire document. Turns out "In XHTML as XML the viewport starts with the document's top element, the html element" (
source. I'm sure I could find it in the W3C spec if you wanted).
If you think about it, for all intents and purposes XHTML web-pages sent as text/html are HTML 4.01 pages with added crap (e.g. the XML declaration when the document won't be treated as XML at all. The XML namespace attribute which will be completely ignored...).
IE is still the most "popular" browser. Even though everyone I know, for the most part, uses something else, the reports I get for my sites tells me that IE still dominates over everything else save for a few, where it is still at around 70%.
I aint got nothing against building pages for IE! When I need a page to work on IE I'd just use HTML 4.01 instead of HTML + the XML crap which won't ever be used (aka XHTML sent as text/html).
Again though, what is the benefit of presenting a true XHTML document?
Oh, this is what you were asking before.
(1) it'll be treated like what it is - an XHTML document. The browser will report an error when the document isn't well formed. The viewport will start with the html element rather than the body element, as per the XHTML specs.
(2) You can use inline SVG, MathML and other XML formats in the document thanks to XML namespaces (I've done this before, plus with XUL. It rocks).
(3) When XHTML 2.0 comes out, you won't have to turn down 70% of your established user base if you feel like using some of it's cool features (XHTML 2.0 will NOT be backwards compatible with HTML, THANK GOD!). XHTML 2.0 has some very nice features and I ain't waiting 20 years for IE to add support (but maybe I will wait a fair few years for the other browsers that actually put effort into standards compliance in every release). See
http://programming.newsforge.com/newsvac/06/01/27/1747243.shtml to learn about some of the new features.
(4) Since IE's out of the picture for the next 20 years, you can consider using XForms (when it's ready) and SVG (already ready) and anything new that comes from the W3C or anywhere else.
(5) A few IE users just might see the light - their web-browser sucks, and get a new one, especially if they find out that XHTML 1.0 is over six and a half years old and Microsoft's IE is the last major web-browser to add support, years behind the likes of Firefox and Opera and even (most likely) Konqueror.
Now, I am NOT suggesting you or anybody else switch your/their sites to XHTML sent as application/xhtml+xml. In general I recommend HTML 4.01, strict if the developer can handle it, when pages must work in IE.