Blurry fonts after upgrading to 10.04, Nvidia issue?

You might be using wrong settings for subpixel hinting - it might be turned on when it shouldn't be, depending on your monitor. I've found that 10.04 defaults to having it turned on with LCD panels (haven't tested a CRT in a while.)

Your panel might be also returning the wrong information about the color order.

Check the Appearance settings. nvidia-settings may override the Free Software stack - there's a lot of points where nvidia driver does odd things. Try temporarily removing the nvidia driver to let nouveau drive the hardware and see if the situation improves.

As of note nouveau in Ubuntu 10.04 does not have 3D acceleration, but is quite fine in 2D.

I've read that in 8.04 all vertical lines in fonts are drawn sharply, but in following releases, vertical lines in fonts are blurred a little. It may or may not be the problem you're having, but it's worth looking at. This blog post explains how to revert the setting.