I had a comparable experience last week launching an online Markdown editor:
and nobody noticed, as I blogged about it here:
http://blog.medusis.com/all-quiet-on-the-western-front-silen...
But I don't think you're right when you say "it's possible that nobody wants what greaterskies offers today. And most of the features that I've been adding for the last week are probably irrelevant." Well, it's possible, yes, but you don't know that one way or the other.
Nothing happened because nobody saw your announcement (or mine); nobody saw it because HN gets hit by a deluge of posts at any time of the day, and luck has a big part in deciding which ones don't sink immediately. (Time of day matters, but time of week matters also; I since noticed that slow days (Sundays esp.) are better for the "Show HN" type of message.)
I think what we need are two things:
- on the functional side, beta-testers that are dependable (as opposed to casual); maybe that means they're paid, but maybe we can do with "honest friends"
- on the marketing side, a story, of which your post is a start (I'm still looking for mine).
Don't give up! and please keep us posted.