Just ran into this earlier.
I'd set my sim to 'Adult' for testing a few things the other day, and left it set that way. Of course, my main av didn't have any problem with this. This morning, I logged in my alt first.... and of course, I'd forgotten to toggle her rating 'choice' to 'PG, Mature, and Adult'. I get dumped into a Mature region.
Of course, this isn't a problem currently, not until the Adult policy start getting enforced, but I can see all sorts of problems once it is - for people who log in after a time away, and find themselves in the altogether (or worse) and dumped into a Mature region.
It'll happen for some people anyway, but shouldn't there be a way to set your account's rating preference on the website?
Currently, you have to login, get bounced from the Adult sim you would have been arriving at, then set your preference, and hurriedly find the LM back to where you had been.
I can see all sorts of AR's against people otherwise...