I, like many others, have lost data due to insufficient (read: none) backups. I am now religious about backups, and have been using LaCie's Silverkeeper to back up my files nightly. All seemed well until recently I had another hard drive failure. I wasn't worried about my home folder, since the whole thing gets backed up, but I did lose all my applications. For the larger ones, you have a box or physical CD, so this isn't a big deal. However, all the neat share - free - donationware I get from various places was gone! I could trace back through preference files, application support folders, or try to remember. This was not ideal.
So I patched together the following simple AppleScript, which I run at startup. It outputs the ls command to a text file in my Documents folder, which is backed up nightly. I can then use this to recount all the applications I may have forgotten about. Paste this code into Applescript:
do shell script "ls /Applications >~/Documents/apps.txt"
I saved mine as an application, and then added it to my login items in the Accounts System Preferences panel.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20061126015107894