I've been noticing that the W's consistently look faded in when "Trebuchet MS" is chosen for the default font.
It's probably optimized for ClearType antialiasing, and we have to (for now, for various reasons) use grayscale antialiasing. A future release (once WPF 4.0 is out) will improve all the text rendering; I'm sorry it probably won't be till around mid 2010, though.
