[Blight]

pirlouy:
We have a 42" 1080p Plasma here at the office, and subtitles look just fine.

Here's why shadow/outline affect the subtitles, as well as the difference between ffdshow sub render and vsfilter.
Shadow and outline can make the font look blurry as they use opacity effects on the edges (which blurs the edges).
VSFilter and FFDShow may not use the same font rendering code (I'm not 100% certain), which depending on the anti-alias setting can make the font look more or less blurry.

And yes, they can be sharper if rendered at output resolution, but it's heavier on the CPU and requires use of specific video rendering technologies which Zoom Player is trying to stay away from.