In the smartphone world you don't need to remember to use the service. Service can use well targeted contextual notifications to remind you when it is relevant. Obscurity is much less of an issue for intelligent services (even if they are rarely used).

I believe that there is probably an opportunity to build these services that have never worked in the desktop world but can work in the mobile world.

Travel planning has other problems (e.g. all the money is in bookings and not itinerary creation). Hotel bookings are super profitable - and hence expedia can spend > $1B per annum on adwords to re-acquire customers.