Rico,

These answers are for DOMESTIC flights only. I have no firsthand experience with International Upgrades.

1A) On Full Fare tix, Plats and Golds can upgrade at time of ticketing. Silvers at 48hrs to flight time.

1B) On discount tix, Plats can upgrade at 72hrs, Golds at 48hrs and Silvers at Midnight on the day of the flight. These upgrades are available IF and ONLY if F class is available. CO breaks it F/C inventory into A class (revenue) and F class (Upgrade).

2) On some routes and days, Plat and Gold makes a BIG difference. On other routes (Hub to Hub or Coast to Coast for example), F seats rarely open up. Making no difference with regards to advance confirmed upgrades.

3) CO does not currently have an advanced waitlist for upgrades. If F class is not available, you either continue to call or wait until you arrive at the airport to be put on the waitlist. This happens to me about 20% of the time and I have only flown coach twice this year (50 Segments).

4) Hawaii counts as an International Destination. (I know, CO has a funny atlas). Hawaii is difficult to upgrade if you are not elite. I flew CO to Hawaii in May. When I peeked at the manifest, at least 1 member of each couple was an elite.

5) I LOVE CO's service. IMHO it far surpasses AA and DL. I have no experience with UA.

Keep in mind that from Chicago, your options to the West Coast are limited. CLE does not have the service to the West Coast that EWR and IAH have. Also, some of the ORD/MDW-CLE flights are on RJ's.

I would suggest that you try looking at some sample itineraries in ITN and look at the city pairs and connecting times. When doing this, keep in mind that a lot of CO elites avoid EWR like the plague. Due to restricted airspace, EWR is very susceptible to weather delays.