I would be dead if I had not used open source. Although Open office is that one exception that is killing me Generally it is heavy for the system becuase it uses java, although if you get used to it there is really few occasions you'll miss MS office.

BTW - it is good to distinguish open source from freeware - in the second one you cannot see the source code and mess with it. But both are very very nice for me since I never get into the code anyway

Another example of open source I use for a long time now and have never been dissapointed with it is FileZilla - FTP client

And I have and open source OS too! Dual boot with Ubuntu Feisty Fog, and almost everything in it is opensource

How about you?