Even in a three-way marginal, unless we know something about how our neighbours plan to vote, you could find that voting for your first choice might end up handing victory to the candidate who was third on your list.
But some web evangelists believe they can solve this dilemma by using the net to build communities with the information to act together to change the electoral outcome.
One site, Count My Vote, asks you to name your preferred candidate - with a guarantee of anonymity - and then tells you how other people in your constituency are voting so you can work out whether it's worth voting tactically.
I can really see the issue here. Though I can't vote in the UK I would vote and support in different ways. For example I generally support Labour. But I doubt I would have voted Labour in 2005 or now. In 2005 I lived on the East End of London and I think I would have made a protest vote for Respect. This would have helped reduce Blair's majority but given that the community has a heavy Muslim population it was a democratic outrage that its Labour representative voted for the war in Iraq, despite the promise she showed.
I now live in North London, and I am pretty happy with our Liberal MP. I would probably vote for her because she has directly helped me and my family.
The complexity of voting in a system where few people actually get to vote for the Prime Minister makes systems like this seem great.
For example the outcome I would want would be a hung parliament over a Conservative majority. The Conservatives are virtually non-existent in my area so there is no danger of them winning much of anything. So do I vote Labour, or should I vote Liberal Democrat? I have on one side a general strategic desire to see Labour retain power. Against this I have personal experience of our Liberal MP and I am very content with her. How would I decide if I could vote?
The web might be able to aid people in making these choices. But be warned, efforts to do this in the US in 2000 failed terribly and Bush ended up taking the Presidency and carrying out 8 years of utter disaster.