Writing Software

I used to subscribe to Writer's Digest (you know, when I actually had time to read it, so before grad school -- now I'm lucky to finish Vegetarian Times and Yoga Journal and those only come 9 times a year).

And there would be all these ads (in Writer's Digest, not the other two...) for writing software.  You can do a Google search and find a whole bunch of software packages.

I don't know how useful I would find this.  Right now, I store all my planning stuff (character profiles, plot information, etc.) printed out and organized in a big green 3-ring binder (I'm the same person who prefers paper books to e-books, though).  And my writing software is called Microsoft Office (Excel for planning/sorting, Word for writing).  Because I already have it and don't have to buy anything extra (grad student stipends are LOW).  Granted, MS Word 2008 for Mac is awful.  I can't even have the spelling and grammar checker active because it causes the program to crash.  And I'm so paranoid that I save every ten minutes.

Does anyone use writing software?  Like it or hate it?  Find one program to be particularly good?  How do you choose a program?  Was it worth the money?