I contacted MSI today to get an answer and I'm very pleased to say that their stance is the same as eVGA's
MSI Tech. 07/12/2010 You can over-volt with the MSI Afterburner software without voiding any warranty.
End User 07/12/2010 Software over-volting won't void the warranty either? Thanks for the swift response
MSI Tech. 07/12/2010 Overclocking via software will not void the video card's warranty. However, any hardware modifications will void the warranty.