I'm not a tax advisor but if the LLC is a single member then it is a disregarded entity for federal income tax purposes. This means that it doesn't need it's own separate tax return, it just gets the appropriate Schedule attached to your personal return.
Lets say you want to start a family owned business and keep your personal assets protected from liability and both you and your wife want to be owners of the LLC. Set up a family trust and then have it be the single member of the LLC and you'll have the LLC protection with a little less hassle of having to prepare an entirely separate tax return for it.
Of course if you're single and own the LLC alone, this applies as well.
http://www.irs.gov/businesses/small/...158625,00.html