because of the rich text format, it doesn't want to let typing. A sort-of workaround that I found, however, was to go into "edit HTML" view where you are able to edit. Hopefully people will be able to type fast enough to make it worthwile to use on the touch.
If you need the apps you said first, than definitely get a Windows Mobile PDA or other PDA/Smartphone. The iPod Touch isn't for you if you need to use those apps on it.