This is a very easy tutorial, but I love this effect.
(This tutorial works in both PS 5.5 and PS 6).
Ok - here it goes:

Open the image you want to add the text to, or create a new one of course :)

Type your text.
This effect looks particulary good created with a white color.

Now drag your text layer down to the Create a new layer tab to duplicate it. Then drag the duplicated layer below the original text layer.
At the duplicated text layer go to Filter - Blur - Gaussian Blur - and enter a radius of 3,9 pixels.

Then go to Filter - Pixelate - Mosaic - Cell size 12.
(You can of course enter any value you want - this is just what I used).

It lookes a little blurry by now so we have to sharpen it up a little bit.
Go to Filter - Sharpen - Sparpen. Do this twice.

Now just apply a nice drop shadow effect to the original text layer and you are finished.

Below you see my final image.
With the blue image I entered 2,5 pixels for the Gaussian Blur and 8 squares in the pixelate action.