The aspell spell-checker does not work in 1.8.
I tried FF2 and IE6 on the Moodle.org support forum area, as well as on my own server.
Instead of the words that are not spelled correctly showing in the pop-up box, the entire contents of the tinyMCE box appear (including any html ... eg. <br />)
The dictionary can not find any relevant replacements.
As the spellchecker files are in the lib area, I selected it ... but inital testing was done in the forum area.