There are two major incompatibilities with respect to previous
versions. First, the \topnode command has disappeared. Now,
everything between \begin{document} and the first sectioning
command goes in the top node, and the heading is generated using the
\maketitle command. Secondly, the preamble is now fully parsed by
Hyperlatex--which means that Hyperlatex will choke on all the
specialized LaTeX-stuff that it simply ignored in previous versions.
You will have to use \T or the iftex environment to escape
everything that Hyperlatex doesn't understand. I realize that this
will break many user's existing documents, but it also makes many
improvements possible.
The \xlabel command has also disappeared. It was a bit of a
nuisance, because it often did not produce labels in the right place.
Now the \label command produces mnemonic HTML-labels, provided
that the argument is a legal URL.
So instead of having to write
\xlabel{interesting_section}
\subsection{Interesting section}
you can now use the standard paradigm:
\subsection{Interesting section}
\label{interesting_section}