Upgrades are one of the most popular perk amongst elite travelers so I'm going to touch on it first.
The biggest thing that lured me over was the upgrades. See, at this point my only experience was with United and upgrades at United weren't exactly easy. With Continental, one could buy a Prestige Pack and have six one-way upgrade coupons along with a slew of other useful goodies (including some miles). But as I found myself flying more and more between the coasts, those upgrades were quite useful. Even though you could only confirm that at the two hour window, I was averaging a 90% success rate. Yes kids, you heard right. 90% success rate on transcon upgrades at the two hour mark.
So, what happened to all the upgrades? A combination of things. First, the introduction of long-range 737s. As Continental introduced the 737-700s and 737-800s, they started pulling the 757s from domestic flying. WIthin a few years of their introduction, the majority of flights from Newark to Seattle, Portland, San Francisco, Los Angles, Orange County, San Diego, Las Vegas and Phoenix were converted to 737s. As background, a 757-200 had 24 first-class seats. The 737-700s had 12 seats and the 737-800s had 14 (later upgraded to 16). On certain flights, we saw a drop of 50% in first-class inventory. The lack of seats created such an uproar that Continental later introduced a sublet of 737-800s that 18 seats (later upgraded to 20) and while this helped the problem, it never made up for the lost inventory. Second, Continental as a company was a far different airline then in the 90s and early part of the decade when it was still trying to woo customers. Continental was entrenched at Newark and had a number of large corporate clients -- so they got popular. Third, with the events of 2001 and later in 2008 we saw a lot of service reductions and with service reductions come few seats. Fourth, Continental realized that even with a reduction in upgrades, the high-yield coach seats were still selling. So why give away something you don't need to?
So, why the history lesson Continental when this is about Delta? To raise some key points as exactly the same thing is happening at Delta.
There is no doubt that Delta has more first-class seats available and thus upgrades will be easier to come by. With the acquisition of Northwest, Delta inherited a huge influx of elites while also reducing the fleet and route structure (when compared to pre-merger numbers). Most of the DC-9s are being retired and many of those are being replaced by regional jets. While these new regional jets have first class seats, the average plane is going from 16 seats to 12 in the front cabin. So, a route that had a DC9-30 or DC9-40 is seeing a 25% drop in first class seats. (Sound familiar?).
At the same time, Delta has decided to attempt to compete with American and United on the high-yield JFK-LAX/SFO market. To do this, Delta removed some of the ex-TWA 757s that were flying European routes. These 757s have a BusinessElite cabin but only 16-seats, down from the 24 seats the prior 757s had. There are already reports of Diamonds missing upgrades on these flights and the upgrade list having as many as ten Diamonds -- that's a huge amount.
So, just like Continental, Delta is reducing the number of seats and is seeing an increase in elites.
For international upgrades, it is common knowledge that Delta's Systemwide Upgrades (SWUs) are worth less than a roll of two-ply toilet paper. Their SWUs are require the purchase of a Y, B or M fare, often running around $2000. At Continental, $2000 will generally buy you a discounted BusinessFirst seat with no upgrade shenanigans. So, why not go for the sure thing? In the summer of 2010, Continental is introducing SWUs as well. The Continental SWUs have no fare class restrictions and are transferrable (which the Delta ones are not).
Elites at Continental have noticed the growing ranks and the ridiculously long upgrade lists (50+ people is average on a Thursday or Friday afternoon transcon). I suspect the same will happen to Delta as the popularity soars.