Anyone with dual citizenship?

That is American and another nationality... How do you travel when you come back to the US? My dilemma is that I will be moving to the UK as an expat but will not be obtaining a visa as I also hold a Spanish citezenship. How do you explain to the immigration officer why you have no stamp or visa? Has anyone ever had this problem? I am just worried because I plan to enter the UK with my Spanish passport and will therefore not have any entries in my American passport. Should I worry or am I just being a bit paranoid?

I am US and Canadian. It is the law that you enter and leave the US on your US passport. That's what I will do. But when I go home to the UK I will use my Canadian since that is where my visa is.

There's a seperate queue at the airport for holders of EU passports.  You just enter the UK on your Spanish passport, and put your US one away.  All the UK is interested in is if you are an EU or UK national, as EU nationals don't need visas. 

There are many, many people with US/other national citizenship and it's not a problem at all. 

When you leave and enter the US, just do so on your US passport. 

If you are questioned in the US, just tell them you are a dual national.  That's not against the law. 

Both of my boys have dual citizenship (US and British) and, as the others have said, they must travel to the US on their US passports.

Thanks for the info all, I think my paranoid side got the best of me 

I do remember reading that the US allows for dual citezenship, and as such you need to enter with a US passport/ its Spain that has a problem with it.  The only reason I did worry a little bit was because when I moved back to the States from Spain in 1995, I was questioned as to why I had no stamp and grilled by immigration before being allowed in.  Seeing as others have done it, I won't worry so much.
Well, there is plenty more to worry about before going to the UK. Thanks again