One of the biggest misconceptions people have about travel is that short trips cost less than longer ones. In reality, a month-long journey is not just cheaper than four one-week vacations; it can in fact cost about the same as one typical one-week vacation. Similarly, taking a year off to travel can easily be a better value (and a more memorable experience) than a decade of hurried, two-week vacations.


More: http://travel.news.yahoo.com/b/rolf_potts/20070129/rolf_potts/rolf_potts19836

This is very true. The bulk of the trip is normally for airfare. So why not stay longer.