I'm pretty sure that Naruto is either related to or is Yondaime. Why on earth would they look and act and be so alike if Naruto was just some random kid. And did you notice that pretty much no one so far in the series has a first-hand account of what happened? We really don't even know how he died. It was 'said' that the 4th Hokage died during the sealing, but there wasn't anyone who was actually there.
Also, during Itachi and Kakashi's fight, Itachi mentions that Naruto is the 4th's 'legacy'. What that means, I have no idea. It could mean that Naruto is his son or maybe because of the sealing he just happens to have qualities like the 4th or it is the 4th. It's too bad Itachi isn't very specific.
Lastly, I'm almost completely sure that Tsunade wasn't married to the 4th. Mostly because she was in love with Dan. Even when she was 50 something when we first see her she's still extremely upset about his death.
