I (basically) did the same thing on Tuesday as I had a meeting downtown in the morning; of course there were no hotel rooms so it was a same day trip.

My meeting ended at 1:00 pm and my flight out wasn't until 20:00 (did this on purpose so I could check things out). I had 7 hours to kill; without tickets to anything it was almost too much time. This was during a weekday, so many of the places were fairly dead during the day. I would expect things to be different if you went during the weeekend.

Take the Canada line to waterfront station. Be aware that Canada line tickets are way more expensive than normal during the olympics, and you can't buy day passes at the machines. A 1-way ticket from YVR is $8.75 but you can buy a 1-day pass somewhere inside the main terminal for only $9.00 (also at 7-11 and pharmasave).

During my 8-hours I walked all over downtown. Saw the torch, walked near Canada Place, walked to BC Place/GM Place, went into the LiveCity area to see the Canada pavillion (had picture taken with relay torch, etc.). I also checked out Robson Square (saw the zip line, etc.) and the countdown clock north of the art gallery. I then went to the livecity yaletown location using the Canada Line (a few hours before the barricade collapse); not much to do when there is no concert unless you want to wait in the massive line for the Coca-Cola pavilion for a few hours. I also took the Canada Line to Olympic Village station to see the Athletes village, but you don't get close and there is not much to see (so don't check that out). I then took the Canada Line to Aberdeen Station and made the 15-20 minute walk each way to see the speed skating oval (again, you can't get close unless you have a ticket). I then took the Canada Line back to the airport and spent about 45 minutes in the lounge before my flight (there was no line at domestic security at all)

Overall, I'm very glad that I took a later flight to check things out and would recommend you make this trip. If I were to do it again I would stay downtown the whole time (maybe go to Livecity Yaletown too) and spend more time at certain places. I would definetly pre-plan all the locations I wanted to visit so that I could plan an efficient route and see numerous pavilions, etc. I would also check to see if there were any events that I could get in to via scalpers/ebay/vanoc site/etc. If I had taken the red-eye back I would have tried to get into see the medal ceremonies at BC place.