Thanks for all your help! None of these suggestions did the trick for me, however :-( I got a number or emails asking me to post a solution if I should ever find one, well, here goes:
This solution assumes, that you got the aspell installation to work. The easiest way to do this is to use Cocoaspell. See the Lyx Mac Wiki for more instructions. The wiki now also states the critical advice that if If at this point you are unable to save new words to the personal dictionary you will need to edit the file at /usr/local/etc/aspell.conf. Remove the line "home-dir $HOME/Library/Preferences/aspell" (line 38 including blanks), or disable it by adding a "#" sign at the begining. I didn't really know how to do this, however, so here's my step-by-step guide: 1) Start Terminal. Copy or type the following line: open /usr/local/etc/aspell.conf This will open the hidden file in your predefined text editor (most likely TextEdit, unless you have donwloaded some editor). (2) Go to line 38 or look for the line home-dir $HOME/Library/Preferences/aspel (3) Add a # in front of the line (4) Chose "File > Open" from the menu to view the file aspell.conf and click once on the file in the dialog box to select it (do not double click) (5) Apple + I (press the key with the Apple logo or command key and the "i" key together). This brings up the "About..." box. At the very bottom, click on the lock symbol to be able to make changes. It will ask you for your administrative password. Now you can change the file to "read and write" in all three instance (just above the lock symbol). (6) After you have made the changes in your text editor (see (2) and (3)), save the file (which you now can. If you haven't done step (4) and (5) you will get the notification "read only." (7) Make sure, that in Lyx you have left the path in "Preferences > Languages Settings > Spellchecker" empty. If you have installed Aspell through Cocoaspell, then make sure that you have /Library/Application Support/cocoAspell/aspell6-en-6.0-0/english.alias in your "Alternative Language" path. All the other paths need to be empty. (8) Restart Lyx. Try the spelling checker now and learn some words. Check the file again. For me, this did the trick. Hope it will too, for you!
