If you have a GP2X, you should go download the firmware. But let me give you some advice, because the instructions are not that clear.
When it says push START and SELECT at the same time as you power the unit on, do not let go of START and SELECT. Keep them pressed throughout the entire update process!
If you fail to do this, it will perform part one of the install (sort of) and just sit at the Loading screen for ever. I pretty much thought I had bricked my GP2X. But it all works fine now.
Great instructions guys. Really. Quite clear.
I will be writing an article for BC about this, as the upgrades are immense, such as: faster booting time, less battery consumption, a new web server, FTP server, Samba Server and Telnet Login among various bugfixes.
It also has a cute little startup chime. I reinstalled the firmware and replaced the WAV with a sound I like (Mac starup chime). Fun stuff.
UPDATE: You do not need to keep the two buttons held down, you just need to turn off the device after the first part finishes, hold down the two buttons again, start the unit, and it finishes the install of the 2.0.0 firmware. Yea, convoluted, isn't it.