I don't know if there are a lot of people interested in these plugins, but here's my (very quick) first impression.
I got the complete collection for Lightroom 2.3 (or higher) a few days ago and it includes Viveza, Color Efex Pro 3.0, Silver Efex Pro, Dfine 2.0 and Sharpener Pro 3.0. The interface is really easy to use despite being an external editor. A RAW image can be adjusted in Lightroom and afterwards edited in any of the plugins. The plugin creates a TIFF or jpeg copy (with lightroom adjustments) that can be edited.
I haven't yet used Viveza, so I can't comment on that. The amount of filters in Color Efex is amazing and can give unexpected and very creative results. Similarly Silver Efex allows a lot of creativity for B/W conversion. Both have special film-filters and a very good way to introduce grain. The grain is of a high quality that can be adjusted to taste. Both Dfine and Sharpener Pro are excellent tools that produce very high quality results.
Here's an example image I created using Silver Efex. (Just a quick edit of an older picture.)