Currently it is getting mixed results with different PS3 Custom Firmware (CFW) versions, including a working confirmation from StanSmith and a non-working report from MiNDTH3G4P.
Feel free to give them a try and post your results (with the PS3 Firmware and version details you are using) in our ongoing thread.
Note: As posted by Easton999GS, be sure to run this application in 1080i NOT 720p or it will black screen on you!
Stay tuned for more PS3 Hacks and PS3 CFW news, follow us on Twitter and be sure to drop by the PS3 Hacks and PS3 Custom Firmware Forums for the latest PlayStation 3 scene updates and homebrew releases!
Not working for me on 4.21 rebug either. I install PSUnban, open the app and click X, then it boots back to XMB and i try to create a new PSN account and I still get the message that the system is banned.