I fly enough to get top-tier status on American, Delta, and US Airways.

American and Delta are earned via miles, while US Airways is earned via 100 segments (mostly US Airways Shuttle service). I say that top-tier status is in general worth it. I don't fly my three airlines exclusively as much to earn status as I do because I really like flying them. Personally, I'd rather connect on my preferred airlines than a nonstop on another. But status does play a huge roll in this.

Domestically, I like upgrades, and US Airways, Delta, and American all have lots of them available to top-tiers. On applicable fares, it is relatively rare for a top-tier to be seated in coach. This isn't true in my experience with United or others. Internationally, I fly Business Class. Delta's BusinessElite business class is great, and I fly AA First Class using a mileage upgrade.

I fly US Airways pretty much all domestically, and they're very good. I like their US Airways Shuttle product. And I think I've been treated very well as a top-tier flyer.

There are tricks to get more status for your money. The main one I utilize is the double-dip deal between American and US Airways Shuttle. About 1/4 of my AA miles come from this deal. But, unfortunately, it only lasts through the end of this year, and it might now be renewed.

I might switch to United, but not right now. The THAI mileage run sounds appealing, and if the merger occurs, UA will be very big in my home airport.