Hi i have a FSC M3438G with 1.73GHz CPU 1 GB ram and 80GB 5400RPM HD.

Some stats for you.

Doom 3 and it runs at about 63-55fps
Quake 4 runs at about 50-45 fps

Detail wasn't cranked up high TBH and res at 1024*768 but this was before I did some stuff.
1. updated the Bios
2. Flashed the GPU
3. Updated my Driver (now 81.94, but will up to 83.90).
Looks like I need to run some more benchmarks.

After this I have played HL2 at native resolution of 1440x900 cranked every thing up bar AA and AF and I am getting a steady 80fps.

I have not encountered the lagging issue, I play games on the machine. ET (Old game most nights) I have F.E.A.R and Far Cry as well and can say that I haven't had problems at all. Maybe I have been lucky, did have to send the lappy back but that was because the GPU and Screen mucked up. FSC got it sorted in a week.
I would say that you get the extended warranty if you haven't lappys are expensive to fix out of warranty.