Snarky comment aside, we've used them for many months and have had a fantastic experience on it. Great for collaboration is significantly better than Google docs/e-mails.
Can you explain why it's better then Google Docs? I've never heard of Hackpad before, but from their front page, it seems like it fills exactly the same space as Google Docs (collaborative, real-time editing), with little information about why they're better.
They don't do a great job of advertising why they're better, but semi-sensible keybindings (similar to Github markdown) and code syntax highlighting sold it for me. Also doesn't require a Google account to use.
Also auto-embeds photos/videos/soundcloud when you paste in links and has prettier UI. Not sure if Google does the former.
It's not snarky to bring up the fact that their site is down and point out that that reflects poorly on their service. It's a perfectly valid criticism.