I think it would be great to add some specific
syntax highlighting for Javadoc comments in the
text/x-java editor. For example, highlighting of
@-tags. More interestingly, highlight (by default,
using boldface) the summary sentence of Javadoc
comments. (Even nicer is to only do so for
comments applicable to public or protected
members, i.e. summaries which would actually show
up in generated API Javadoc.)

I used to highlight the summary sentence in
Emacs's Java Mode, and it was very useful when
editing API classes for their Javadoc, since you
could spot the relevant descriptions very quickly.

I will attach a portion of the
java-font-lock-keywords-3 that I used in Emacs,
for purposes of comparison. (I stopped using it
for performance reasons; the regular expressions
were not well optimized.) Basic syntax: list of
highlight matchers; each is a list of a regexp
(quoted string, Emacs-style RE so \( not ( is the
grouping operator etc.), then list of highlights,
each being a regexp group number, then a font
modifier, then prepend and override flags (adjust
precedence rules).

Note that in JDK 1.4 the summary sentence is no
longer computed by a simple English-only
algorithm, but using BreakIterator and a
locale-sensitive algorithm. So I think the
highlighting should follow the semantics of
BreakIterator, to ensure that Javadoc comments
written using the NB editor will appear correctly
in generated HTML.