With Ubuntu 9.04 it became easier to use the Nouveau driver with Ubuntu Linux as a snapshot of its DDX driver (xf86-video-nouveau) and its kernel DRM code were packaged up and made available through its package repositories, which continues to be the case in Ubuntu 9.10. Though after the Ubuntu Developer Summit last week for 10.04 "Lucid Lynx", Canonical is now going to put Nouveau into the kernel by default. Not too many details beyond that or their intentions are known at this time, but Nouveau developers are currently being asked about the matter.
One mailing list message can be found here. Pekka Paalanen of the Nouveau project has commented and recommended they use Nouveau's kernel mode-setting support and goes over the Nouveau project's official release steps of first needing to get this code in the mainline kernel's staging tree and then to tag and release their libdrm and DDX driver code once this support is available in a released driver. The Linux 2.6.32 kernel is likely what will be found in Ubuntu 10.04 LTS, so for this release Canonical's kernel team will likely end up pulling in their own Nouveau support regardless of whether Nouveau enters staging in the next few months.
Having the Nouveau driver with all of its kernel mode-setting glory by default in Ubuntu 10.04 would be certainly welcomed and would be a much better option than continuing to use NVIDIA's xf86-video-nv driver that only provides basic 2D acceleration atop an obfuscated and ill-maintained code-base and that's about it (the xf86-video-nv tree hasn't even seen any serious work done in months) with no kernel mode-setting or support for other newer technologies.
For Ubuntu Lucid we will likely not see Nouveau's Gallium3D driver appear for providing OpenGL acceleration by default for this NVIDIA hardware, but even just a proper 2D driver will be quite exciting and a huge step forward. This will also mean that a majority of the graphics cards (ATI, Intel, and NVIDIA) would all be supported by kernel mode-setting in this next Ubuntu release. To see how the Nouveau driver is currently working with your NVIDIA hardware, one easy way to test it is by trying out a Fedora 12 LiveCD that has a recent snapshot of Nouveau. Also worth noting is what the X stack in Ubuntu 10.04 may look like.