Going from Sprint to Oly--What to expect?

What to expect depends on a lot of things.  Weekly training volume.  Competitive background in any of the sports.  Etc.  Coming from the perspective of someone without a competitive background, and someone who was losing some weight, and someone with a year or so of sprints under his belt, I found the distance to be materially longer.  My suggestion for your first Oly is to keep it aerobic.  You'll go anaerobic in a sprint.  But for your first oly, just keep within yourself.  Keep the HR down.  And see what you've got left in the last 5K.  If you're still feeling good then, let it rip.

Good luck.

I don't want to be alarmist but, after looking at your training logs for the last few months, I'd say your training volume does not support being properly conditioned for an Olympic distance triathlon.

Your swim volume is very low, IMO. So is your running. It's kind of late in the game to increase those volumes and make the necessary adaptations that your body needs to make.

Making the jump from a sprint distance swim to an Oly distance swim takes conditioning. Being able to swim 1,640 yards nonstop and then calling it a day is one thing. Swimming 1,640 yards then jumping on your bike for 26 miles (followed by a 6mile run) is quite another.

When was the last time you were continuously aerobic for 3.5 hrs? That is another way to look at it.

Nutrition and pacing become much more important the longer the expected race.  For a sprint, eat at home a couple hours before you start the race, and you can finish with just drinking water on the bike/run.  As you start getting past 2 hours, you need to make sure you've got some glucose floating around in your bloodstream still, so you should plan on taking in some calories.  Gatorade *OR* a gel or two on the bike should give you enough to finish the run.  If you haven't tried exercising with either, do so in training. 

For pacing, don't worry if you might be finishing in 3:30 when last year's last-place finisher was 3:27.  That isn't an unreasonable time for the race, but you may feel pretty lonely during most of the run.  Now if you thought it might take you 4 hours, get ahold of the race director.  Olympic distance races may not have official cutoff times, but he should know that he'll need volunteers longer than he did last year.  Many OLY races will start the awards about 3 1/2 hours after the start of the last wave.  If you're in the last wave, they might start without you, but will usually stop the awards to recognize your finish.  If you're in an earlier wave, you may cross the finish line before other participants even if you have the slowest time of the day. 

How big do you think the field would be if every prospective "last place finisher" chose not to race?  The 3:30 person (you) opts out and last year's 3:27 finisher does too.  Pretty soon, the only people racing are the ones who think they can win.  

I found my first Oly to be much more difficult than I anticipated, so prepare to suffer a bit.  Then again, I am no great athlete nor do I put in a ton of time.  I struggled greatly in the swim, took longer than normal actually due to hyperventilating and swerving, and was WIPED heading to T1.  Try to avoid that   I was worried about being last and completely lost it.  For a not super strong athlete, you must control the swim.

I did a sprint yesterday, after getting used to longer races.  In a sprint, the swim is VERY hard.  Like GO GO GO the whole time, breathing heavier than I usually would in a swim, etc.  The swim in an Oly, however, is when you start to think about staying steady and getting from buoy to buoy.  Don't totally give up on the speed, but think of it more like "I am going to finish this without expending all my energy".  I would recommend keeping the kicking to a minimum and keeping your heart rate and breathing down.  Then, you will still have your legs at close to 100% for the remainder of the event.  My pace is generally 2:20-30 per 100 this year.  I remained very calm and did my most recent Oly swim in 36 mins, and felt good (a 10 min PR over that first race). 

In general, jumping to a new distance is about survival for the casual triathlete.   For this first one especially, it's less about "racing" than it is about completing each leg and keeping it together.  VERY different from a sprint.

Good luck!