After waiting for a resolution (which didn't happen) and ranting online about it (which had no effect), at the 25th of November I sent this bug report on MySpace:
According to Wikipedia, more than 1% of web users use a resolution of 800x600 or less on their web browsers. If those users come to MySpace, they'll be able to log in, but not to sign out (because the "Sign Out" button will be always not visible).
As you can understand, this is an huge security flaw, which MySpace must solve as soon as possible. As it is, it would better not let them log in than forcing them sto stay logged in.
 - http://en.wikipedia.org/wiki/Display_resolution#Current_standards
Since until now I've got no reply, I'm posting this in the hopes that the issue gets more exposure. Wanna help? Please send yourself a similar bug report, and spread the word!