Hi, I did a SFO-JFK-CDG-DFW-SFO last July by purchasing a regular (and by regular, I mean discount, not full fare Y) ticket and then using a 25SS award for each set of flights. My dates were firm and I was going those days regardless, so I ended up being put on the standby list for the upgrades both times. I also requested the upgrades late (within 2 or 3 weeks of the trip) and had to pay an expedite fee. Luckily, my 25SSs were both put through before I left, and I had a wonderful trip. That trip started my gold challenge, and I subsequently became platinum.

Having gone through what I did back then, here is my list of "lessons learned":
- Definitely see if inventory is available for the upgrade. Anxiously waiting to hear if I would spend 14 hours in coach really took a lot of my energy being nervious. Then again, maybe I'm just spoiled. =) (though I am ruffing it to ZRH and back in a few days)
- Get to the airport early. Not only is it an international trip, but they have to re-issue your ticket when they apply the certificate (or something similar). When I did this, there was some strange issue with my ticket that kept me at the first class check-in counter for almost an hour, and that made the line behind me really really long, too!
- Enjoy the lounges, since you are flying in a premium class. Don't be afraid to show up early. Also, be glad you are towards the front of the line getting off the plane waiting for customs, but don't count on your "premium/priority" checked baggage to come out first. My bags, and another couple who were also in "Business first" and had those lovely orange priority tags on their bags were among the last to get our bags from the flight -- not sure why, other than hearing that baggage handling at CDG isn't spectacular.
- More bag troubles -- my bag got lost somewhere in the hand-off between customs in DFW and getting to SFO that delayed my bag to be on the next flight in... and I had consciously packed some items I really really wanted that evening, so my last few hours after arriving in SFO were spent waiting for my bags to maybe show up... don't pack anything you NEED immediately upon landing.