Hello,
Implementing spell check seems like one of those obvious features. Doing so is extremely expensive from a development perspective. We are constantly weighing the cost of implementing features against one another including doing the work to add spell check. It is still on our radar and we're discussing when and how to implement it.
In the meantime, there are some spell check tools available on the app store which might be something to look into. I would also encourage you to visit the IdeaStation and kudo the spell check enhancement there. http://forums.autodesk.com/t5/inventor-ideastation/2-words-spell-check/idi-p/5023978
Tom Rang
Director of Engineering (Customer Engagement)
Product Design & Manufacturing
Autodesk, Inc.