I have a CentOS server on my network. I intend to use the PI as a thin client for that. If it can run Quake III then I reckon it can run NX Client plenty fast enough. Fully fledged browser, email, apps/docs on the big screen TV.
Even if I have to shell out half as much again on a BT keyboard/trackpad, I'd still have larger screen, better compatibility and more typing comfort than I would on a tablet and for a fraction of the cost.