| The killer for me is file format. I got burned once by a program that used a proprietary file format -- when the program went kablooie and I found out the company that made it was no more I was hosed -- and all my data went bye-bye.
Save it in text files, rtf files, html -- but don't pack it into some binary format that nobody else can read.
Word to the wise.
For features, I don't want "drill-down" functionality, really. What I want is quick access to disparate items -- to be able to switch from my campaign calendar to my NPC description, or whatever. To be able to create and group items. To be able to print items out for reference at the game table. | 
And yet another word from our sponsors
