Which leg of race least/most important?

Bike, because it is where you spend the majority of time in the race.

x2

I attended a Joe Friel workshop a couple of years ago where he suggested you appoach a triathlon as a bike race proceeded by a swim and followed by a run.

Mark

For me, it would be the swim.

Here's a case in point: When I got back into tri, the first race I did was the Satsop sprint tri. I only did 2 weeks of swim training prior to the race. I ended up winning my AG (the field wasn't all that deep), but came out of the water in 3rd place. The next year, at the same race, after a full year of training (which included regular swim training), I came out of the water in 2nd place, but only 3 seconds faster (but I was minutes faster in the bike and run).

Full year of training, 3 seconds over 800m.

YMMV.

I don't know the answer to your question, or that there is one, but here is a possibly relevant consideration, at least for me and maybe for others.  I did my first tri on Saturday.  I was competitive on the bike and run (nobody passed me on the bike; one person passed me on the run; I passed several people on both -- this is less impressive than it sounds, because my swim was 68th out of around 150.).  I ended up third in my age group.  On the swim, I lost over 3 minutes to the age-groupers ahead of me.  By the end, I was 2:35 behind the winner in my age group overall.

In other words, if I had a clue how to swim, things could have gone much differently.  I feel that if I had to choose where to focus, it would be the swim.

I agree with tcovert poster...

 As long as you are a relatively decent swimmer, the swim is the least important.  I have been told (and also from personal experience) that it takes a lot of practice to improve swimming. 

Biking is most important - that is the longest leg of an event.

For running, esp. in a sprint distance, I think your focus should be on getting comfortable with the bike to run transition, rather than running lots of miles.  Most people can get through a 5K.

I can't believe some one has already posted this great advice

the left leg

This would be the correct answer the majority of the time because, as stated, it is clearly the longest event (time wise) on average. A 10% improvement here would total the most time.

I have to disagree with this point. Hillary Biscay just won IMWI yesterday in the swim. Her bike leg and run leg were slower than that of the second and third place finishers. The swim leg is becoming more and more important in triathlon.

Right, but I think this guy was looking for advice on having a decent time in a sprint and not winning an ironman.  Big difference I think.   

I suck at biking-I am pretty good at swimming and ok on running. You know where that gets you? bottom half/third. In an olympic race each MPH faster on the bike is worth 4 minutes. Each minute per mile you drop running is six minutes. If you improve in swimming from a 2:00/100 yard to a 1:45/100 yard you get 5 minutes but 1:45 to 1:30 only 3 more minutes. You get diminishing returns faster in swimming in my opinion. When I get 3-5 minutes coming out of the water I give it all back and more when people are able to go 2-5 MPH faster than me. I cant eat all that up on the run.

(Big issue is that I enjoy swimming and running and tolerate biking)

I focus more on the run, because it is what I can fit into my schedule easiest and gives me some sort of fitness for the bike.  Then swimming whenever I can fit it in.  The bike takes the hit and is trained the least.

But I do have a few thousand miles of cycling road racing in my past that I get to fall back on for "base" so my bike splits are still usually pretty decent.