Since I can remember, all the Linux distributions always has a less than good defaults fonts (or maybe it was just my imagination) so I always has to change the fonts. The good news is Ubuntu change this, they now have a new type of fonts (Designed by Dalton Maag)
The Ubuntu font (family) is open-type ttf based font format and fully unicode compliant. It contains Latin A and B extended character sets, Greek Polytonic and Cyrillic extended. The font has been hinted for superior screen display. Its spacing and kerning is optimised for body copy sizes.
You can visit the Ubuntu blog for more info about this new feature, to do this just follow the link in the bottom¬
Source: Ubuntu Blog