The original tutorial was found at http://www.state-of-entropy.com/ under PSP 5, and can easily be adapted to GIMP with minimal differences.
Using GIMP 2.6.11
Open any size drawing, with a white background.
Use any font you wish, but rounded fonts work best.
My drawing is 640 x 480, using Cooper Black font @ 150px centered on the drawing.
Save a Path from Text, after centering the font in its permanent location.
Right click the text layer and choose "Layer to Image Size".
Merge the text layer down onto the white background layer.
Duplicate the resulting layer. You should now have two black text on white background layers.
Select/highlight the bottom-most layer and run a Gaussian blur of (12 px).
Now run Emboss (Filters/Distorts/Emboss) using the following settings:
Select/highlight the top-most layer and change the layer mode to Difference.
TIP: Also check out Overlay and Soft light modes for making pretty awesome 3D text.
Add pattern layers or color layers (do not fill selections with color or patterns on the original layer) and choose Hard Light or Grain Merge for your layer mode. Feel free to experiment with the different modes to see their results.
Using the text path, I inverted the selection for the background, then created a second pattern layer for the text with the path selection not inverted, using Burn as the layer mode.
This is the result:
That's it. Enjoy! :)