Hi iDad -
I've been using Topaz products continuously since a year or so after they first hit the market. I have almost the entire set (bought them one at a time), and I would say that I probably use at least one of them in every "winner" image of mine that's going to get published / printed, and that image needs individual attention in the areas of artistic enhancements, stylization, and occasionally to help correct lighting problems (eg, reining in excess local contrast, evening out the distribution of light over a scene, etc.)
In addition, I have been in friendly correspondence with Eric Yang on and off since around 2008. In fact, I suggested to him that he modify "Detail 2" to include separate adjustments for "lights", "shadows", and "overall" to position his product favorably against Nik's "Tonal Contrast". He incorporated these features in the next release of "Detail".
I am fortunate to have a huge number of photography related software products at my disposal, and am even more fortunate not to be financially constrained ( within reason ;-) ) in my choice of software, so I use whatever I find to be best for the task, and Topaz products often are the best choice for me.
However, I do a lot of event work for my employer, and will often shoot several hundred images in one session and be under time pressure to get them out. In fact, just yesterday, I edited about 1700 images from the spring, getting them prepared for fall publication.
That's the one situation where I wouldn't dream of using Topaz. It is not even on my radar screen when I have to crank out a large number of images in a limited period of time. In the last couple of years, IMHO, the best choice for such jobs is clearly Lightroom. Before LR3, I used Bridge and ACR. Before then, I don't even want to think about it (and Topaz wasn't even a gleam in Eric's eye back at the university). LOL.
Any you asked a very good question and I hope I was able to convey how I use their products.
Cheers,
Tom