The site became unresponsive for about twenty to thirty minutes just now for paid users, and maybe some free users as well. It looks like another website search engine started hammering the calendar views of paid account holders again. I firewalled off their IP range and the site seems to be back now.
I'll keep watch for a little while to make sure I got all of their IPs blocked, but I believe I'll be contacting the company soon so we could unblock it again.
(I don't give out the names of these things because I don't want to potentially hurt their business or get into some other trouble.)
Update: Just shot a second crawler hammering calendar view. I think we might need to adjust some things on the site so they can't do that anymore.