I'm a pragmatist. My software is almost entirely released under a free license, usually the GPL, but hardware? I'll buy whatever is cheap/available/suitable.

Still, each to their own. If you want to buy only free hardware, with open-source BIOS, firmware, and all that good stuff I wish you luck.

If you're building a new desktop, why put in an add-in card from the one of the three graphics vendors least compatible with Open Source? For that same £30 you could have upgraded to a system board that included integrated graphics, which would work far better.

I just built a PC for my father, and used exactly the same Nvidia GT 610 card you chose -- the 'lspci -nn' line is identical, including the "(rev a1)" part. However, I'm having a different experience because I'm using KDE4 rather than Gnome 3.x. In KDE4 using the stock Nouveau drivers, many of the 3D OpenGL features work.

Additionally many of the compositing features work, but a few don't; KDE4 reports that:

"KWin Window Manager
The following desktop effects could not be activated:

o Blur
o Cover Switch
o Startup Feedback"

So from this I gather that the Nouveau driver supports some OpenGL features, but not all of them -- so that's what I think is going on when it comes to your experience with Gnome 3.x going to fallback mode.

For now I'm trying to stick with the Nouvau driver to see whether my dad will be happy with it -- on other systems I use the proprietary Nvidia driver. One of the features you might look into with the proprietary driver is underclocking the videocard for thermal/reliability reasons. For instance on my laptop I use this in my xorg.conf file:

Section "Device"
Driver "nvidia"
Option "NoLogo" "1"
# Following option sets max power saving on both Battery and AC
Option "RegistryDwords" "PowerMizerEnable=0x1; PerfLevelSrc=0x2222; PowerMizerDefault=0x3; PowerMizerDefaultAC=0x3"
VendorName "NVIDIA Corporation"
BoardName "Quadro FX 570M"
BusID "PCI:1:0:0"
EndSection

@Anonymous:
Using a videocard built into the motherboard means you can never upgrade it, and it's typically something I and others want to upgrade. Additionally (and ironically), RMS himself suggests using an Nvidia card because the Nouveau drivers are the most open.

Nouveau works just fine in both KDE and GNOME with full desktop effects activated. I see two possible causes for the problem.

The first possibility is that the 610 (aka 520) is simply too weak, and the proprietary drivers can make better use of its dismal power.

The second, and IMO more likely, possibility is that the drivers are simply too old. My 560 doesn't work on Wheezy, but works on pretty much any distro that is using kernel version 3.4 or later.

You could try the latest stable Fedora (either 18 or 19, due to be released in the next couple of days), as they have a couple of Nouveau developers on staff and in general are much more up-to-date than Debian, even Sid. Alternatively, you could try a newer kernel on Wheezy; Liquorix makes Nouveau work on my 560 in Wheezy, for example. Or just upgrade to Jessie.