At least for the time being. It's causing a great deal of different problems for many Mac users.
Keep an eye out at Engadget or Gizmodo (or even Apple) to find out when the issues have been fixed. For the time being, stick with 10.5.5.
More info:
Mac OS X 10.5.6 Users Report Crashes, Blue Screens -- InformationWeek
Mac OS X 10.5.6 Update Crashing Users' Systems - News and Analysis by PC Magazine