Posting this here in case anyone else has this problem. I installed Autodesk Product Development Suite 2013 on a freshly unboxed Dell Precision M4700 (plenty of horsepower). Autodesk Inventor ran extremely slowly and took 100% of one CPU core, or around 30% of the total CPU. The other Autodesk apps in the suite ran quick and smooth.
Lot's of troubleshooting later - the fix is to NOT use a custom font scaling in the OS. Once I changed the display text size to Medium 125% (the default) the problem was resolved.
Hopefully this note means you won't have to go through what I did, but here's the deets if you care: I set up my new hi-res laptop with Windows 8 and thought the default system font size of Medium 125% was too big so I changed it to 110%. Then i proceeded to install all my software on the laptop. Inventor barely ran on the new laptop and was way faster on my 3 year old laptop so I knew something was wrong. I ran Process Monitor from SysInternals and it showed that Inventor was getting a Buffer Overflow error on a particular font. The error occurred repeatedly and was causing an endless loop. I uninstalled that font and when I rebooted my system font was replaced by some weird font. So that's when I discovered the problem was related to the system font. And once I knew that the problem was fixed in minutes. This all took place over about 6 hours of multiple full uninstalls, test profiles, changing permissions, registry investigations, etc.