As far as bash is concerned, no, there is no difference. In fact, the manpage has them share the same definition
declare [-aAfFilrtux] [-p]
[name[=value] ...]
typeset
[-aAfFilrtux] [-p] [name[=value]
...]
Declare variables and/or
give them attributes. If no names are
given then display the values of
variables. The -p option will display
the attributes and values of each
name...
I also found this little tidbit which further substantiates my claim as well as the ksh
portability you mentioned.
The declare or typeset builtins,
which are exact synonyms, permit modifying the properties of variables.
This is a very weak form of the typing
[1] available in certain programming
languages. The declare command is
specific to version 2 or later of
Bash. The typeset command also works
in ksh scripts.