IIRC, the official builds of OOo have always used semicolons for separator. Some third party builds offer the "enhancement" of using commas, to look more like Excel.
Also, when opening Excel files, the transition to semicolons has never been an issue.
The issue arises when users come from Excel to Calc, need to enter formulas with functions, and use the period (dot) as the decimal separatot. (Roughly half of the world uses comma for decimal separator, and for those countries, Excel also provides the semicolon for parameter separation within functions.)
For those having the issue, the change will not be a great transition. Most people will get used to it in virtually no time.
OOo 3.3.0 and Apache OOo 3.4.1/4.0.0, on Ms Windows 7 and Mac OS-X.