Seems like some update recently broke spellcheck in IE on the desktop only. Verified on my desktop and laptop. Both spellcheck and autocorrect do work in the Metro browser, so I'm guessing it might be some addin that is interfering with spell check.
Just wondering if anyone else is seeing similar behaviour? If you don't, could you also mention if the Office 365 preview is installed, and what antivirus is active on your system?