Yeah, it felt pretty much like this.
Ahh, the joy of post-patch Addon shenanigans. 5.0.3 has been mostly smooth for me addon-wise, with one noteworthy exception: 3-4 second lag spikes whenever anyone on my Real ID/Battletag friends list signed in or out. By lag spike, I mean complete game freeze for a few moments.
Not a big deal, right? It's just a few seconds. Sure...until that's 3 seconds of standing in a fire in a raid, or 3 seconds of letting some horrible rogue dismantle you in PVP. And if you have a lot of people on your list, or they're doing a lot of switching characters (who would EVER be doing THAT after major patch, huh??) then you just get slammed by these bursts of lag, over and over again.
It's like being stun-locked. BY THE GAME.
The worst part about this was that for a few days, I didn't even know Real ID was the problem! I have RiD notifications turned off, so it just seemed like utterly random bursts of lag, with no explanation. I could be fighting a boss, I could be checking my mail, I could just be flying around the world - it made no sense to me. It wasn't until I experienced it a few times when I just HAPPENED to have my RiD list open, and notice that immediately after unfreezing, a name would have disappeared off the Online list...did I finally realize they might be related.
After browsing the forums and getting nowhere, and (more significantly) asking TWITTER and getting nowhere, I decided to see if it was actually something to do with an addon. So via trial and error (turning on the addons one at a time, logging in, and seeing if I froze when someone logged), I did eventually track down the culprit...Postal, the extremely-useful mailbox addon.
It's funny, too, because I had actually paid some attention to Postal when I was updating my addons. It hadn't been updated - oh no! - but, fortunately, the 4.3 version still seemed to work! And it did work. For mail. I didn't realize that, for whatever reason, it would start choking on battle.net sign-ins and be murdering my game.
I really did not want to lose Postal. Luckily, turns out there's now a 5.0 update, just a few days old! So if you're also having these lag spikes, try grabbing the latest version and see if that fixes things. And enjoy playing the game without your friends inadvertently killing you!