The Launcher applet for the Xfce panel doesn't just launch applications. You can also use it to launch files that you open regularly. Examples might be a Gnumeric spreadsheet with expenses, a big Abiword document you are (slowly) writing, or an often-used shell script.
The trick to getting Launcher to open files is to use the xdg-open command. Suppose you have a file called 'Girlfriend.txt' in the folder /home/[username]/Letters/2010/.
1. Right-click on a panel.
2. Choose Add New Items...
3. Choose Launcher from the list of items.
4. Enter 'Girlfriend' in the Name field.
5. (Optional) Enter a brief description of the file in the Description field (like, 'Draft love letter').
6. In the Command field, enter
7. Click on the Icon box to pick a suitable icon from the many available choices (like, a big red heart).
8. Click on OK.
Now, when you click on the heart icon in the panel, Girlfriend.txt will open in Mousepad.
The xdg-open command will open any file using the default application for that file type. To set the default application for plain text documents (for example), open Thunar file manager and navigate to a folder containing a '.txt' file. Right-click on the .txt file and choose Open With>Open With Other Application... From the list of available applications, choose the one you want to set as the default '.txt-opener', make sure the box next to 'Use as default for this kind of file' is checked, and click on Open.
Close the opened file. From now on, xdg-open will open all '.txt' files with that same default application. Unfortunately you can't have a panel launcher using xdg-open which (for example) opens one particular .txt file with Mousepad and another panel launcher which opens a different .txt file using Abiword.
Great tip!! If I may, I use something similar. Instead of xdg-open I use the name of the program. I have some files that open with mousepad and one that opens with OpenOffice Calc.
All of these and more are in Quick Launcher in the panel. Just another option if you want to use different programs for specific files.