Usability 
I've been playing with Tripit.com lately, it's a startup with a really clever but simple approach to travel planning. You don't even have to register, just forward the confirmation e-mails that you get from airlines, car rental agencies, Orbitz, Travelocity, Amtrak, Eurostar and hundreds of other travel companies and websites to plans@trippit.com. Tripit parses the e-mails, including attached PDFs, and builds an itinerary for you, complete with historical temperatures, maps, and links to information about your destinations from Wikipedia and other sites.
Tripit's mobile version is pretty limited. It gives you read-only access to your itineraries, displays "Closeness Alerts" and lets you share trips by email. That's better than nothing, but I'd really like to see Tripit flesh out the mobile features. Travel is by definition a mobile activity, when I travel my phone is my PC. Travel plans change, even in the middle of a trip, but none of the Tripit features that are usable with a phone (feeds, iCalendar integration, "Tripit To Me", mobile web site) let you plan or edit trips. I tried using the full Tripit.com site in Nokia's WebKit, Opera Mobile 8.65 and Opera Mini 4.1 and I was able to view the site and enter some trip details, critical tasks including adding flights were impossible.