I was in Mallorca for a few days last week. The railway line that runs from Palma to Soller is not what you could call a straight line. It runs through tunnels and winds through mountains, but gets to the right destination. Speeches don't have to be a straight line either. Traditionally, you tell people what you are going to tell them, tell them, and tell them what you told them (the traditional "business sandwich"). Often a series of slides takes you along the path from start to finish, making it tough to deviate at all.
Some display software, such as Prezi allows
the creation of a presentation from chunks of information that don't
need to follow in any particular sequence. However, delivering a
non-linear presentation is not about software, it's about an approach
which many speakers find uncomfortable. Increasingly, audiences are
demanding a style which is more than just a procession of slides, so now
is probably a good time to think about your speech structure.
Not every speech lends itself to a non-linear style. Not every audience
will appreciate it. Furthermore, you must still have some kind of
overall structure and aim, otherwise you will simply be presenting a
mass of information with no overall message. Delivering in a non-linear
way may demand more preparation and more subject knowledge than a linear
narrative. It may also require what a pal of mine used to call "a big
dose of brave pills".
Many stand-up comedians are masters of non-linear delivery. They can
deviate for minutes at a time, but still return to a core message. They
may tell stories in a different sequence each time they speak,
responding to prompts or questions from the audience, or just how they
feel. In my opinion, the more interactive and non-linear you can learn
to be, the more people will want to see you speak. You can choose to
ignore the trend, but the train may leave without you.