What went wrong in this sunset shot?
Is it that I focused on the sea instead of on the landscape?
Or is it a too long shutter speed (I had it on auto)?
Or it's just the lack of tripod?
http://images.gorillarape.com/hosted/20100607142701sunset.jpg
Could be a few things. Yes, a tripod would help with slow shutter speeds. Especially if you were zoomed out. Also, depends on your cameras metering. ie, how it measures the light and where. In that pic it is a high contrast photo, so most cameras will battle a bit.
EDIT: genius here didn't look at the data. Your ISO was too low as well. Should be easily 800 or possibly 1600 in those conditions. And 1/6 shutter needs a tripod. No question.