You've seen the situation a thousand times. There's a limited window of opportunity to perform some task - for example, all citizens are required to pick up new IDs within the next three months - and although everyone knows that there'll be a huge queue, everyone waits for the very last day, creating a huge mess. It's almost as if all people are masochists by nature, secretly enjoying the fact that they'll have to wait for hours in the queue (and then complain about it) although they could have easily avoided it.
In the world of web startups, there's an opposite, yet eerily similar situation. Summer is the dead season, and weekends are no better. Everyone who has something to say, waits for September/Monday morning to do it, thus creating a huge noise in which some of the good stuff inevitably gets lost.
And yet here I am, looking for a lead, a development or a story and bashing my head against the desk cause there are (almost) none. On that first Monday in September I'll have to discard 95% of what reaches my inbox, and now I'd be happy to find any half-decent new web application.
Of course, not everyone can take advantage of this weekend/summer slumber. If you're a well known company, you're probably looking for some mainstream media coverage, and then you'll be better off sending your press releases on a work day.
But if you have a cool widget, Facebook application, mashup, or something similar that will only get picked up by blogs, why not be one step ahead of others and send the news about it when everyone else is resting? Unlike mainstream media publication, most blogs don't know about weekends, holidays, summer, or day and night: anything goes. And not only that; bloggers are hungry for breaking new stories, and many of them will be paying extra attention over the weekend when some of the other bloggers are away.