Looking at the aspell www page I see this,
-----
A patch for ispell.el for improved Aspell support also available. This patch
will notify aspell of the replacements one makes so it can improve the
suggestion list in the future. A more involved patch can be found here This
one also adds UTF-8 support but will only apply cleanly to Ispell.el 3.7
beta.
-----
Just let you know that for aspell >0.60 emacs22 has full support including
aspell dicts parsing and default utf8 use. I modified emacs22 ispell.el and
put it in Debian so emacs21 does benefit too. Unfortunately xemacs seems to
not support [:alpha:] regexps, so does benefit less from the improvements.