I believe this bug applies to fonts on all platforms with antialiased fonts and is present in all current versions of Tk. In tk8.*/generic/tkFont.h, TkFontAttributes.size is an integer. So tkFont's converting between pixels and point sizes is inaccurate. Also, with modern Linux font support, the user can type in non-integer point sizes for fonts in the standard font choosers.
For example, on Fedora 7 with gnome:
$ gconftool-2 --get /desktop/gnome/interface/font_name
Nimbus Sans L Condensed 11.5
% tk scaling
So is that a 16 pixel or 17 pixel high font? What if it were 11?
The request is that TkFontAttributes.size be changed to be a float.