I travel a good bit: not as many as some folks I know (such as Scott Schnoll, Tony Redmond, or other members of the far-flung Exchange tribe), nor as much as I used to, but at least a couple of times a month I’m on a plane heading somewhere– often to Huntsville to see my sons.
On my last trip I had a bit of hassle occasioned by a crew availability issue. The problem: I have to be at my office all day (long story), so I need as late a flight as possible on Friday. That means the 2:20p departure from SFO to Dallas, then a connection on to Huntsville.. but with only a 40-minute connection time, any serious delay ex-SFO means I’m going to be stuck.
I thus decided to try TripIt Pro. I have happily used their free service for several years; it’s the best way that I’ve found to organize and keep track of travel itineraries. All I have to do is forward confirmation mails to plans@tripit.com and they magically appear in my mobile client, neatly sorted by trip and time. The Pro service costs $49 a year, but it offers several interesting features, including an alert service that promises to notify you of delays and the ability to notify you if the fare for a trip decreases.
This morning, I called American at about 9:45a to request an upgrade for my 2:20p flight. I got that done with no problem. By the time I got back to my desk, here’s what I saw in my inbox:
Sure enough, due to SFO weather (which was delaying inbound aircraft), my outbound flight was delayed by long enough to make me miss the Huntsville connection. The “Alternate Flights” link showed me all of my flight options, and I was able to call American and get an agent to rebook me to an earlier flight. Notably, at no time did American themselves send me a notification of the delay– no text message, no e-mail, no nothing. This is despite the fact that I’m signed up for, and usually receive, flight status updates from AA.
While I admire the potential of getting a notification telling me “oh, your fare decreased,” the notification feature just saved my bacon for this trip– well worth the $50. If you travel more than a few times a year, I strongly encourage you to look into TripIt Pro (which has a 30-day free trial). I am now a convert.
Paul's Down-Home Page 
I can’t say enough about TripIt Pro. I’ve gotten gate change notifications just as I was entering the airport. This is great because it usually means a change in the direction through the airport. Saves me wasted time walking from one end of a large airport (like DTW), to the other.
As you mentioned, changes in flight status including delays, cancellations, and other notifications come much quiicker, and with better information than those that come from the airlines.
The point tracker feature is nice as well, as it gives me a snapshot of my various points programs.