FWIW, I don't think the issues right now are load so much. I think there's some insanely bad logical pieces that are messing things up, and possibly have corrupted accounts that were created early on. I base this on a few things.
1. The "username" requirements.
The username is case sensitive. Choose a username that is 6-74 characters long and must contain a lowercase or capital letter, a number, or one of these symbols _.@/-
Really? I know some systems use case-sensitive usernames, but given that you're already forcing some odd characters and whatnot in there, why not normalize to lowercase? This just feels like it's going to cause more support problems (mobile safari automatically uppercasing a username that should be lowercased, etc).
Also... the English description of that username is nowhere near intuitive. "A lowercase or capital letter". As opposed to what other kind of letter?
2. Multiple accounts with a single email address.
I've been able to 'successfully' register multiple different username accounts with the same email address. When I do a password reset based on email (the couple times it worked) which username was I resetting the password for? I say 'successfully' because no login attempt has ever worked. And now trying to register yet another username with the same email address doesn't work, but the error message is so vague ("there was a problem" IIRC) that I can't tell if that was a factor or not.
OK... 2 things. That's about as far as I've been able to see in to the system so far, so that's all I can judge it on. But it seems that they've probably allowed some logical inconsistencies in my own signups that may be causing more problems now, and I don't think they are related to load.
Of course, I could be 100% wrong, but it doesn't feel like load is the culprit right now.