Gartner Analyst: Stop Outsourcing Now
While this article is written in the perspective of US, it is still worth reading. One interesting point to note is "multi-sourcing", instead of plain vanilla outsourcing.
I'm pretty fortunate to have a company which believes in putting extra thoughts before outsourcing for the benefit of 'cost savings'. In fact, according to my observations, the service level that a vendor provides is not as good as your own IT staff.
Plus, that's always a cost attached to your vendors when one needs extra work done; while your own IT staff would gladly go out of his/her way in order to fulfill those demands.
Just my $0.02.