The shot on the right, of my son's 1890 Dutch Colonial farm house with a complicated lacy skyline is what I use to test masking techniques and Photoshop masking plugins (click on the image to see a large version). I've added the garish Spanish blue sky just so it's easy to see how the details of skyline mask come out. It's just a test situation, the sky is never this blue in the Northwest.
A few days ago David Lenhert pointed out that Topaz had introduced a new masking plugin. What every real estate photographer wants is a quick and easy method to mask skies and interior windows. Most masking techniques work great on simple boundaries that have a nice high contrast edge. The real test comes when you are in a hurry and have a skyline like the one in this photo with intricate low contrast branches on the sky boundary. So I got out my test image and put Topaz ReMask to the test.
Topaz ReMask has a little steeper learning curve than other masking plugins. It's really an action more than a plugin. Once you get the hang of how to use it, it's quite easy. Topazlabs.com has a good tutorial video. On my test image above, I found that as long as the laciness in boundary line is not too wide the plugin works nicely. The place where it fall apart on this image is when you try to get it to mask a wide swath. For example, the edge between the sky and the large Cedar on the right side of the image does not come out as nice as it does when I use the blue channel masking technique. Topaz does do a pretty good job on the low contrast lacy trees on the left edge of the photo and around the chimney. These kind of trees give most techniques a hard time.
Conclusion: I'd say Topaz ReMask is one of the better masking tools I've tried. It has problems with some situations but, all masking tools have their quirks. As you can see, you have to look at a big image to see the defects. In a 300 or 400 pixel wide image like you'd use on the MLS it's hard to see any defects. I think it's worth the money. I'm going to purchase a copy.