I'm currently running an nForce based board (MSI K7N420 Pro), and the support under Linux has been a bit of a mixed bag.
First, the good. IDE and USB worked perfectly right out of the box. I'm using the integrated video which also worked with no trouble with the standard nVidia drivers.
Now for the not-too-bad.. the integrated NIC was supported a short time after I bought the board (I bought one of the first few nForce boards that were actually available on the market). It has mostly worked, though it is a closed-source driver, so naturally my kernel complains about being tainted. I've heard some people complain about some problems with the NIC driver, particularly with reference to ARP, but I use it only in a VERY simple setup (home LAN with 3 computers, one of which is a gateway/firewall that all traffic goes through).
The sound card support is also kinda weak to say the least. It's only used as an AC97 card, which is a far cry from the true potential of the built-in sound chip. I also found that with the precompiled drivers I only get sound from one speaker. However I did download the source tarball and install that way, and it then works ok as a low-end audio solution. Sound is fine, though it doesn't seem quite as crisp as it sounds in Windows (maybe that's just my imagination, I haven't done any real objective testing).
I've also had a real odd-ball problem related to nForce and my Adaptec SCSI card causing the kernel to lock-up, but I believe that is entirely related to how Mandrake compiled the Adaptec driver into their pre-compiled kernels (note that this problem is NOT related to the nForce drivers at all, it happens whether they are loaded or not).
So, long story short, I would expect Linux support for the nForce2, but not to the level that Windows is supported. It would be nice to see nVidia release good quality Linux support for the nForce, but I'm not holding my breath just yet.