Here is demo: http://jsfiddle.net/ENqy6/
There are 3 cyrillic letters inside .rur div.
Custom font ‘Rouble’ transforms the first letter to rur sign and hides other two letters (glyph width set to 0).
It works fine. But ie8 displays two last letters as spaces! Guess its .EOT font format issue.
Any thoughts how to fix it?
Tried similar code in IE6 @ Windows XP and it seems fine, no added spaces:

I edited your fiddle to
hello<span class="rur">руб</span>hello.