The first time I ran Linux was in early 1994, In 1995-1996
I switched to it as my primary OS, and I've used it as my
primary OS since then.
Since then lots of interesting things has happened and
Linux has become a major player.
In 2006, I went to Mac as my desktop OS. It has been an
interesting experience.
One of the first things I did when going to Mac, was to
find out about a few VERY good opensource applications.
A good starter is http://www.opensourcemac.org/
I have also been involved in Bazaar since sometime in 2005
(By involved, it means that I have mostly been lurking and
bugging the developers :) ).
Bazaar is a distributed revision control system that really
rocks. There are many of them popping up now, but I think
Bazaar is the most interesting one for the future.
Also, check out my bzr extmerge plugin.