I wrote about Hookpress a few weeks ago, and I think the idea has some potential uses. Mainly, though, I think it might be useful for someone who just isn't familiar enough with WordPress and/or PHP to write their own plugins directly, or for someone who already has an external event service set up and available via HTTP. But also, if enough stand-alone services pop up using the webhooks idea, it could catch on for certain tasks.

Granted, it's not something that tons of people are bound to use for lots of tasks, but I can definitely see it being a really quick way to let WordPress events trigger external scripts, rather than writing a full-blown custom plugin, and dealing with the extra memory and blocking time, or having to re-invent the wheel every time.l

I think if you read Anil's Pushbutton Web post, the key point is that this concept "pushes complexity to the hub".