I was in the same situation, I didn't like how the new way images were
either being cropped or stretched. and i couldn't get it to function
like before. i didn't want to re-add phpthumb either. in the magic
fields plugin, there is a file "MF_thumb.php". the new images sizing
is mostly in here it looks like. it also looks like they based much
of the code on some internal WP image_resize functions. but not 100%,
if you replace line 118 to line 174 of MF_thumb.php with this code (is
from the WP internal resize function), you might get the results you
are looking. it works for me...
//new code (borrowed from wp)
// don't crop, just resize using $dest_w x $dest_h as a maximum
bounding box
$crop_w = $orig_w;
$crop_h = $orig_h;
$s_x = 0;
$s_y = 0;
list( $new_w, $new_h ) = wp_constrain_dimensions( $orig_w, $orig_h,
$dest_w, $dest_h );
}
brandon