The underlying solution is of course the same for ConTeXt and LaTeX: you need to have a way of changing what macros do such that they write the correct output rather than typesetting. This is also much the same as tex4ht does. The advantage ConTeXt has is that the macros are provided mainly by one focussed group, and they include the necessary 'back end' to make that conversion easy. To do the same for LaTeX, you need to handle all of the macros that might be present, which is a problem given the number and variety of LaTeX packages. So while in principal it's possible, the implementation is a severe challenge.
(With my 'LaTeX3 hat' on, this is an obvious area to bear in mind when defining an updated format. To do that, you need to have a much more 'regular' syntax and input than is often the case with LaTeX files at present. Again, I think ConTeXt shows how this can be done as it is already good on keeping the input within it's own structures.)
ConTeXt does not directly output XHTML, it outputs XML. However the current browsers (at least Opera, Firefox and Chromium) are able to display XML correctly. The XML can be styled using CSS.
When you want real XHTML, you have to transform the XML to XHTML using external tools. ConTeXt standalone ships with an example file: texmf-context/tex/context/base/export-example.{tex,css}. Here is a modified and shortened version of this file for demonstration.
% file example.tex
\setupexport [width=470pt, hyphen=yes]
\setupbackend [export=example.xml, css=example.css]
\setupbodyfont [dejavu]
\setupinteraction [state=start]
\setuplayout [width=middle]
\setupwhitespace [big]
\definedescription [description] [width=broad, alternative=hanging]
\definemathalignment [gather] [n=1,align={middle}]
\starttext
\startchapter [title=Example]
\startparagraph
\input ward
\stopparagraph
\startparagraph
You'll find more information on the ConTeXt garden.
\startfootnote
The ConTeXt garden is the ConTeXt wiki.
\stopfootnote
Another option is to contact the mailing list.
\stopparagraph
\startplacefigure [title=Some cows]
\startcombination[3*1]
{\externalfigure[cow.png][width=3cm]} {medium}
{\externalfigure[cow.png][width=4cm]} {large}
{\externalfigure[cow.png][width=2cm]} {small}
\stopcombination
\stopplacefigure
\startdescription {Ward}
\input ward
\stopdescription
\startformula
x_{1,2} = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
\stopformula
\starttabulate [|l|r|p|]
\NC And \NC here \NC comes \NC \NR
\NC a \NC table \NC \input ward \NC \NR
\stoptabulate
\stopchapter
\stoptext
And here comes the corresponding CSS file, that is responsible for the styling in the browser.
/* file example.css */
document {
font-family : "DejaVu Serif", serif ;
font-size : 12pt ;
line-height : 18pt ;
max-width : 50em ;
padding : 1em ;
}
paragraph, p {
display : block ;
margin-top : 0.5em ;
margin-bottom : 0.5em ;
}
section {
display : block ;
}
sectioncontent {
display : block ;
margin-top : 1em ;
margin-bottom : 1em ;
}
section[detail="chapter"], section[detail="title"] {
margin-top : 3em ;
margin-bottom : 2em ;
}
section[detail="chapter"]>sectionnumber {
display : inline-block ;
margin-right : 1em ;
font-size : 3em ;
font-weight : bold ;
}
section[detail="chapter"]>sectiontitle, section[detail="title"]>sectiontitle {
font-size : 3em ;
font-weight : bold ;
}
description {
display : block ;
margin-bottom : 1em ;
margin-top : 1em ;
}
descriptiontag {
float : left ;
clear : left ;
margin-right : 1em ;
text-align : left ;
font-weight : bold ;
}
tabulate {
display : table ;
margin-top : 1em ;
margin-bottom : 1em ;
margin-left : 2.5em ;
}
tabulaterow {
display : table-row ;
}
tabulatecell[align="middle"] {
display : table-cell ;
text-align : center ;
padding-right : 1em ;
}
tabulatecell[align="flushleft"] {
display : table-cell ;
text-align : left ;
padding-right : 1em ;
}
tabulatecell[align="flushright"] {
display : table-cell ;
text-align : right ;
padding-right : 1em ;
}
tabulatecell {
display : table-cell ;
text-align : left ;
padding-right : 1em ;
}
combination {
display : table ;
margin-top : 0em ;
margin-bottom : 0em ;
}
combinationpair {
display : table-cell ;
padding-right : 1em ;
}
combinationcontent {
display : table-row ;
text-align : center ;
}
combinationcaption {
display : table-row ;
padding-top : 1ex ;
text-align : center ;
}
float {
display : block ;
text-align : center ;
margin-top : 1em ;
margin-bottom : 1em ;
margin-left : 2.5em ;
}
floatcaption {
display : block ;
margin-top : 0.5em ;
color : rgb(60%,60%,0%) ;
}
floatlabel {
font-weight : bold ;
margin-right : 1em ;
}
floatnumber {
font-weight : bold ;
}
formula {
display : block ;
margin-top : 1em ;
margin-bottom : 1em ;
margin-left : 2.5em ;
}
sup {
font-size : xx-small ;
line-height : 0 ;
vertical-align : top ;
}
Here is a screenshot from the PDF version:
And this is a screenshot from the browser:
As you can see, the style is pretty close. It can be further optimized through tweaking the CSS file. Included graphics, of course, have to be present in a format that the browser can handle.
Hyphenation is also present. ConTeXt inserts soft hyphen (0x00AD) characters where hyphenation is possible, which enables the browser to justify the paragraphs.
The resulting XML can be displayed by browsers and e-book readers. However, not all e-book reader are compatible, especially when it comes to math. Browsers also have their problems with displaying math.
Best Answer
Pandoc supports converting Latex to Epub. I don't think there's any "black box" solution producing high-quality output, but the HTML that Pandoc generates is easy to work with.
Resources:
John MacFarlane's Creating an ebook with pandoc
My answer recommending Pandoc(now deleted, so included inline below) to SO question, User manual for Java software: In-application help + PDF, which also discusses some other useful technologies for dealing with Epub conversion.