I think that travel time is a really important factor in making an MMO feel like a world instead of a game. However, travel time is highly inconvenient. So I was musing about ways to incorporate travel time into an MMO, and came up with the following design.
Goal: An MMO where travelling between two towns takes one week of real time, without boring the player to death.
1. Have the actual travel be tied to an NPC that continuously moves, rather than the PC.
Having the player get on a horse and travel in a straight line for hours is just not going to work. So we need to have something do the traveling for the player. My basic idea is a caravan. The caravan starts at the first town, Antwerp, and travels to the second town, Brussels. The player signs up for the caravan at Antwerp, and the caravan takes seven days to travel to Brussels.
Whenever the player logs in, she logs in with the caravan, and can adventure in the area around the caravan's current location. The player moves much faster than the caravan, but the distance between towns would still require hours of travel time if you went directly.
2. Have the travel be tied to the guild level, not the individual.
One of the problems with long travel times is that it is easy for a group to get separated, and then be unable to play together. So the easiest thing to do is to move as a guild. Here, instead of the individual players signing up for the caravan, a guild officer signs the guild up, and the entire guild moves together. That way, even players who haven't logged in for a while still log in near their guild.
I think these two ideas would go a long way towards making travel time more palatable. You still log in and can easily group with your friends. You aren't spending all your play time riding a mount in one direction. But you still move steadily. Movement time for everybody is the same, regardless of playtime.
But moving, and travel time is a big deal. It's something you prepare for, and don't undertake lightly. A caravan bringing a guild with goods from another town might be very important economy-wise, if resources are not distributed equally. I think it would go a great deal towards making location important again.