Nice work, I've been using regular NV for a few months now but this is the first version of nvAlt I've used. Looks great! I see a few tiny bugs (I use the normal notes-on-top view):

<ul>
<li>The alternating row colors are not the same height -- white rows are taller than the shaded ones. (23px vs. 15px)</li>
<li>The first row is shorter than the rest (16px vs 18px) -- causing it to feel too close to the top (I measured this by selecting the row while alternating-colors was turned off).</li>
<li>The results area scrolls up one pixel every minute or so that I'm typing in the main window. I think it happens every time it auto-saves? The scrolling stops when I stop making changes.</li>
</ul>

Doesn't seem to be working. The preview jumps back to the beginning, and my typing issue isn't actually a delay, but a pause. Sometimes when I stop typing, the last character won't appear until I press another character. So, so that seems a separate bug from the delay, which I guess I've not noticed.