you can currently run some emulators in it, namely a version of MAME and a SNES emulator too. It comes with a standard web browser - Firefox, Openoffice Suite (like MS Office but free) and an IM client for all major IM systems.
You can also set-up media streaming, although that may not be needed for much longer.
What $ony are trying to do is allow an open system for developers (hobbiests) to create some interesting games / emus etc, although they haven't allowed access to the 3D hardware as yet.
The one proper hack for the Xbox 360 has been used to get Linux to boot on it yet the PS3 comes with this as standard. I think its a great idea just not utilised as much as I would like.