I was going to write a similar app myself, but thought
I'd check sourceforge and sure enough, qnotify does
what I want.
A couple features I'd like to see:
1. allow specifying negative x-y positions so we can
right justify on the screen.
Such as -geometry 400x100-0-0 (why not honor the
standard geometry arguments?)
2. allow adding a drawn border inside the notification
to make the box stand out for cases like transparent.
actual window decorations aren't necessary, just a
highlight or shadow to define the edges of the box
when the color blends with the background.
Nice app though, I'm already using it.