Update: The new firmware update 2.41 for PlayStation3 is now available for download. It appears that there are no new features in this firmware over 2.40, it simply addresses the problems that that many users experienced last week. You should probably head to the official Sony PlayStation boards and see if any other issues arise before deciding to update.
After the short-lived and quickly pulled 2.40 release of the PlayStation 3 firmware, a lot of people were hit by flaws with the released that caused the console to malfunction. Sony did mention that as soon as they fixed the issue they would re-release, and according to recent reports they are planning to make it available this week. This will be the 2.41 iteration, and will hopefully fix all the issues associated with the 2.40 release.
Not everyone that got 2.40 in the short time it was available experienced problems, but unfortunately for a few it resulted in dead consoles. The new 2.41 firmware should contain the same updates for XMB access among other things that the 2.40 release was supposed to bring.