The card works well; have not attempted to setup dual heads.
I had to use a kernel boot parameter to get the fb working: append="video=matrox:vesa:0x118"

Read the matroxfb.txt in the kernel source tree under Documentation/fb

Not only does this card work well with linux but Matrox offers a driver/tool that lets you set up dual heads with a nice GUI interface. Also they have an online discussion forum for Linux users using Matrox cards where you can get most any question answered.

Back when I used the Dual Head feature I found out that you cannot use the card's 3D support (ie playing Tux Racer, etc) while in Dual Head mode. This is NOT a driver/Linux issue but rather a hardware limitation of the G400. The same problem exists under Windows. If you need 3D writch to single head. Although i haven't tried it I suspect that you can set up the dual head stuff without the Matrox software as well.

worked great, did not ever try dual heads in linux, dual monitors worked in win2000 though, rather nicely. virtual desktops reduces the need for that some imo. mandrake 10 detected it on install and there were no problems.

No problems with this video card. I am very impressed with the ease of installation in Linux. If you need a good video card to get running with very little effort, then this is the one for you.

No problems at all, works great for general use. I haven't attempted dual head or fb though.

For general use, the card is OK, but there is a major bug in it's driver what makes it completely useless for Blender. An other annoying bug of it is the occasional crashes when switching to and back from console mode. Not recommended for ones who rely on either of these, otherwise it is OK.