Server update delays - SLS-1.23 troublesome?

Linden Lab has delayed the planned update of Second Life server systems to SLS-1.23 this week, which was originally to take place on Tuesday, Wednesday and Thursday. The pilot deployment did not appear to roll out as planned on Tuesday and the schedule was pushed back one day to Wednesday, Thursday and Friday.

Now this has slipped again to Thursday, Friday and Saturday. The questions that immediately come to mind are, what is so dire that it is causing the delays, and what is so important that the update can't be pushed back to next week instead of these incremental delays?