2 languages at the same time?

What does /lang/ think of this? I've seen various views, some say that as long as you don't study them back to back, but rather spaced apart by a few hours, it's fine. Others say they tend to get confused and jumbled, and it slows down learning of both tongues.

What does everyone here think? Has anyone tried learning two or more languages at the same time? How much time did you put in to do it, and what were the results?

If they're related wait until you get intermediate level in one before starting the other, if they aren't you can start at the same time but I'd still wait until I was intermediate in one.