I have encountered 3 problems in the past week - in order of serioysness:

1)
Now receiving the pesky "we don't have an email for you" message. everytime I log in, despite the same email address Delta has send thousand's of messages and tickets over the years still being in my profile.

2)
On a trip, SLC-ORD - leaving and arriving on time, last week -I wanted to check-in on-line for the return flight the day after once at mhy hotel, but was unable to do so. The mesage received was that the flight from SLC-ORD had been delayed to the point to where I needed alternate flights, and all I could get up for that reservation was a list of early morning flights SLC-ORD, not of much help given that I was aleady in ORD. Called Delta who after shuffling me around to 2 other agents failed to fix/clear it so I gave up. Was only able to check-in once I was in the airport.

3)
Wanted to make a reservation in BE SLC-CPH for April 2010 and got the desired routing and price (I fare), but each time I tried to ticket it, I received a message that the fare was "gone" and to try again. After 3 tries with the same thing happening, I tried to search on "schedule" rather than proce, but backed off when the cheapest fares listed were "S" fares (for the same itinerary where there were plenty of I-fares when searching on price), >$1000 more than the I-fare I wanted. Called Delta and made the reservation the old fahioned way with the correct I-fare I was unable to ticket on line.

This latter one, I believe, could be a serious priblem for Delta if a non-aligned customer just moves on to the next airline when unable to purchase a desired premium ticket on-line at Delta.