I recommend using big and wide characters for this effect (so it looks much better).
First start a new RGB image. Create a new alpha channel in Channel Palette (Window >Show Channels) by clicking a "New Channel" icon.
Type your text using type tool. I recommend using a big and wide font. Deselect.
Make a copy of that channel with your type by dragging the channel over the "New Channel" icon in the channel palette.
Filter >Blur >Gaussian Blur >3.0 (you might want to use a bigger value if your type is VERY BIG).
Make a copy of channel #5 (this creates channel #6). Switch to channel #5 and Filter >Other >Offset, enter -1, -1. (Here you can also use bigger values depending on the size of the type)
Switch to channel #6 and use same filter but with settings 1, 1.
Now time for channel calculations. (Image /Calculations...)
You get a result in Channel #7. Switch to it after calculations are done.
Now, Image>Map>Invert. Then Image >Adjust >Auto Levels.
Now comes the artistic part of that effect. Choose airbrush tool in toolbox, set pressure (in Options Palette) to 6%, pick a big brush (45 pixels wide or so) choose black as the foreground color and make some sprays over your text. Notice that the areas that you will leave unpainted will be shinier after you finish the effect. That might require some practice and patience.
Actually, on the sample image you almost don't see those black sprays (they are more like light gray than black). But the thing is, if you do the lines any darker everything will be messed up after the next step; so be careful.
Here, the dark lines may be hard to see but with the following step will intensify them. Then Image >Adjust >Curves and draw a curve similar to one on the image shown. (They add reflections to the letters.)
Now it's almost ready. Select>Load Selection>#4. Select >Inverse. Fill it with black (Edit>Fill...).
Then load the selection again (Select >Load Selection >#4). Now Select >Modify >Contract>3 pixels. This option may also change. This will be the bevel for our letters, so look for yourself. Select >Inverse. Then Image >Map >Invert.
Ok, we have a letters ready. Select>All, Copy to clipboard, switch to RGB channel and paste there.
Now we gotta colorize those and drop some nice shadow, but first load selection #4 again and copy it to clipboard. You can switch to RGB Channel and fill it with some nice texture or whatever you want. I left it white in this example. Paste the characters, Image >Adjust >Variations..., choose a nice colour and then drop a shadow. (A free copy of the drop shadow filter is included in the demo of EyeCandy plugins - see Downloads page).