1) The US is trending toward economic downturn. The success of airlines is largely tied to the prosperity of the US economy. Granted, nobody knows how long it will last or how bad it will get.

2) US carriers are in a transitional period. Legacies are in merger talks and two regionals have gone out of business so far in 2008.

3)You said it... oil prices. This is a big deal for two reasons. First, it will constrict the general state of the US economy even further. This, of course, means a reduction of demand for air travel. Second, airlines may respond to high fuel prices by increasing fares and increasing load factors. To accomplish this, a reduction of capacity (and pilot jobs) will likely be necessary.

The party is over. If it's your sole desire to work for an airline this decade, I'd get on board now. But be prepared to wait out a long career as an FO, take pay concessions, get furloughed, survive a merger, or some combination of these. If you're a career changer, give it some serious thought.

But that's just my opinion, and you know what they say about opinions.