I have lurked around these forums for a while but felt I would finally enter a discussion as I have something to contribute.
I purchased Topaz Details recently and have found it to be great value. I used Lucisart 3 before that but was wanting to upgrade to a 16 bit application. It was (much) more expensive to upgrade to Lucisart 6 that handled 16 bit and gave some more control over the effect. Topaz Detail handles 16 bit and has excellent control over the efect. Lucisart I found tended to add alot of contrast and sometimes a colour cast whereas Topaz allows me to adjust this aspect to my taste. Very nice I for what I want.
As some have mentioned the effect can be over the top but if used gently it can increase the clarity of the image to a point I find acceptable.
If you want an idea have a look at the landscape section of my site. Most of these were treated with either Lucis or Topaz. Some are quite obvious in the effect but this is what I wanted. Others are a bit more sublte. It is all about how heavey handled you want to be.