As you know, the previous update, made some loose their Contacts and Calendar Entries.
Now what RIM cannot bring back, they have prevented it from happening in the future for the 4G PlayBook.
This OS is mainly for that, no new update in it. Nothing great, but usual bug fixes, and makes the entire device slightly faster.
So what are you waiting for?
Get your PlayBook on the charger, and update to OS188.8.131.528 and let us know how it goes!