I use uniform thumbnails on my site:
http://www.viperalley.com/gallery/sh...ry.php/cat/504
and it works just fine. I use the most current Imagemagick (what version is yours?) and rarely find a bad thumbnail. Make sure you have a current version of IM and understand that when using a script like IM to resize a 1440x900 image to a 100x63 thumbnail there is going to be some loss of quality.
I don't see a bug here that can be fixed on our side since the thumbnail is a product of ImageMagick.
Maybe you should consider using bigger thumbnails? Like 120 or 125? I use them on ViperAlley and get great results.