If you can't login, then something went seriously wrong.
Fun fact: in our 7.5 year history, that's never happened. However, it's happened to facebook, twitter, myspace...basically every other large social networking site.
The core issue is usually cross site scripting (XSS issues) and the related API"s on those services.
Nope, if you track (as we do) the history of exploits on other sites...it's ONLY b/c of 3rd party API's and XSS :)
We pay a lot of attention to these things. (kind of our business to do so, lol.).
Another reason for that could be that this site isn't as popular as those sites, just saying =P