The Group Program Manager of SQL Server team finally announced the news last Friday (Saturday Morning SL time): There will be new service packs for SQL Server 2005 and SQL Server 2008 before end of the year.
SQL Server 2005 sp4 is expected to be released by the last quarter of this year, but the mainline support will end by April 12, 2011.
SQL Server 2008 Sp2 is expected to be released by the third quarter:
Here is the link http://blogs.msdn.com/sqlreleaseservices/archive/2010/02/12/sql-server-servicing-plans.aspx
As you all know, service packs are simply the collection of Microsoft's cumulative upgrades (CU) released after the last service pack. However, service packs go through much deeper quality assurance tests than cumulative upgrades. As a reason, many companies do hesitate to install cumulative upgrades to their production and critical installations. However, with this announcement, many many like to install the service pack.