The two main limitations:
- Processing power.
- Software library.
Now I will play devil's advocate by arguing with my own points.
- Processing power. In a way it seems silly to say the Pandora doesn't have enough power. It has plenty. My first desktop PC had an 8mhz CPU, and for many years I was happily running Windows PCs ranging from 200mhz to 800mhz. The average person could still get away with an 800mhz PC for everyday use, if the world wasn't full of bloated software or the otherwise inflated 'need' for power.
- Availability of software. The Pandora software library isn't too bad actually, when you include the Angstrom apps. Outside of gaming there is a good range of productivity & networking options. Run Debian from an SD card and you've got access to many thousands of apps.
One limitation that is hard to get around is wear & tear. The Pandora doesn't have a lot of easily replaceable parts. If you wear out the nubs or break a USB port, expert repair is required. Not that I'm saying these things will definitely happen, but if you're relying on the Pandora as a primary computer, the down time is going to be many days or weeks.
Depending on your needs you could make it your primary PC, but I think most people will agree it makes a better sidekick.