Three different Windows machines running two different releases of MS Explorer report serious problems displaying my blog when I tried using Liberation Sans size−2 for Body Text. The other two custom fonts were set to default. When I set the Body Text back to default, the problem goes away. The error is "invalid argument" similar to what is detailed below.
I also use custom CSS customization on top of the Twenty Ten template in case that is a factor. With or without custom fonts there are CSS errors according to the w3org validator. But the generic Twenty Ten template already generates CSS validation errors before any CSS mods.
Example error details
User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)
Timestamp: Sun, 19 Jun 2011 23:17:41 UTC