The battery life depends on the fact you have a 6 or 9 cells battery and if you use the Eco Mode or not.
Actually I hav'nt use the battery yet (just doing the test right now).
The 6 cells battery is said to last about 3 to 4.5 hours depending of the use.
8 hours is for the 9 cells battery.
If you have 4 GB RAM, what you can do is to disable virtual memory and use the SSD tweaker utility. That should encrease the battery life.
http://www.techspot.com/downloads/4926-ssd-tweaker.html
With my Acer Timelife 1825PTZ and a 6 cells battery (and touchscreen) it is said to last 8 hours in Eco Mode and with the standard HDD. But with my SSD it last about 10 hours in power mode Internet use (Wifi and Bluetooth always on, screen and SSD never sleep and light 100%). ^^
The difference is that the Acer has an Intel GPU (4500 HD), while the MSI has a ATI Radeon ! That makes a big difference.
Six month ago the price of the MSI X600 (with SU9600, 4 GB RAM, 500GB HDD and 9 cells) was almost 1000 € and I paid 558 € (about 719 USD) some days ago for the same machine, but only with a 6 cells battery)...
That may also explains why I have no bag and no mouse ?!?!?!
How much have you paid for yours and what is the configuration ?
I'll tell you about my battery life when the test finish (Power mode for the moment) and after I finish to test different modes (at least the Eco mode).