Hey Jon...
Late to the party (just finished working on my TAXES!), so a belated welcome, too.
I, too, am a hearty supporter of layer mask techniques. Once I started using them, I felt I'd discovered an exceptionally flexible (and non-destructive) method for experimenting w/o screwing up an original layer!
In addition to the selective application using black and white as DJ noted above, you can also use the opacity and blend mode settings to further fine tune the effects of the layer (with the layer mask) and the layers below it. Just what you need, right? More options, more flexibility.
Besides painting white or black on a regular layer mask (I normally "airbrush" B or W for feathering/blending purposes vs. the hard edge one with get with a regular paintbrush), one can use the same techniques on adjustment layers as well. Doing so enables one to selectively apply "the adjustment" to layers below.
To illustrate with a not-very-practical example:
1. Create a Hue/Saturation adjustment layer on top of any color layer.
2. Drag the Saturation slider to the far left, resulting in a grayscale image.
3. Now choose the airbrush tool (pressure: 25%-35% or so) and a fairly large, soft-edged brush set to black.
4. Start painting on the adjustment layer...
See how the color starts coming back (or more accurately, how the black suppresses the desaturation effect) on the layer below? Works the same with any adjustment layer. It's a great way, for example, to bump up the saturation of lips and eyes w/o affecting the rest of the face.
OK...enough on layer masks. You're probably tired of the pitch by now.
Back to blurring, for $200, Alex.
A couple other filters that are in the same ballpark as Gaussian Blur, but achieve slightly different affects with varying degrees of control are:
* Blur/Smart Blur (tries to retain edges while blurring the rest, with varying degrees of success)
* Noise/Median (ditto)
* Noise/Dust and Scratches (a different spin on smoothing)
Depending on your needs the effects you're trying to achieve, these may (or may not) come in handy in your blurring arsonel.
Anyway...good luck and again welcome aboard.
~DannyR~