On the Xbox 360, the launch patch has improved texture loading times, various issues that could cause the game to lock up, and a glitch that played multiple tutorial videos instead of just one. Client prediction has also been fixed, which stops "rubber banding" in online games.
The PS3 patch is similar to the 360, with an added fix for host migration and the Ability Wheel, which was showing the wrong class abilities. You can get this update through a connected PS3, even with the PSN still down.
On the PC, there have been issues with the game corrupting character data. This has been fixed, and a better crash report system has been implemented. Splash Damage is working on resolving any hardware compatability issues that players might be having.
In addition, the team's still working on Brink's biggest problem -- lag. This is holding back the 360 version, and the studio knows it. Hopefully it's fixed soon, because I am still playing Brink beyond my review, and I want it to kick as much arse as possible.