Before you ask, no, I'm not going to reveal how to crash a realm in just a few simple steps. It would be chaos. However, there is, in fact, just such a technique making the rounds of the internet. Hopefully it will be fixed very soon -- one commenter I've seen says that his realm went down four times in 20 minutes. I'd say that qualifies as a serious problem. If you've been having realm stability issues lately, perhaps some jerks performing this exploit are to blame. And Blizzard? Please get this fixed ASAP.
How's your realm been?
P.S. If you know the exploit, please don't post it here. Realm crashing is not cool. If you do post it, your comment will be deleted.
Update: Blue says a fix is on the way, without actually saying they're fixing a player exploit.