failure of auto increment in inndb (mysql)

I read this on the django project site: 

Since MySQL 5.5.5, the default storage engine is InnoDB. This engine is fully transactional and supports foreign key references. It's probably the best choice at this point. However, note that the the InnoDB autoincrement counter is lost on a MySQL restart because it does not remember the AUTO_INCREMENT value, instead recreating it as "max(id)+1". This may result in an inadvertent reuse of AutoField values.

Now to my newby senses, this is a huge problem. How can you have a primary key, or a foreign key, without the assurance that they are unique? But I did some searching around the net, and while there are some suggested fixes here and there, no one seems to be in a panic about this. So, my question is, why? Are unique primary keys not as important as I thought they were? How are you dealing with this, if you use mysql/innodb? Is this a reason to jump to nosql? Help me wrap my brain around this. Thanks.  

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