I've played around with a demo a little bit. The control-points are pretty innovative (if not brand-new; Nik licensed the tech to Nikon a year or so ago for CaptureNX). They make certain types of selections a breeze, that might otherwise be pretty difficult.
Having said that, the actual tonal and color controls in Viveza are somewhat crude, particularly thh color-balance controls (Red, Green, Blue sliders) which I found way too coarse to be of much use for subtle editing.
The other sticking point is the price. Control points are a novel feature but IMHO they don't come close to justifying the $249 price tag. Consider that CaptureNX sells for half as much, contains all the functionality of Viveza, and is also a full-blown RAW convertor. Granted, CaptureNX is only of use for NEF shooters, but to me it still seems like Viveza is vastly overpriced compared to most other filters.
I guess if you're in business and need to regularly make the kind of selections that control-points are tailored for, it could pay for itself in time saved. But I would strongly recommend trying out the demo before purchasing to see if its functionality would really justify the price tag for you.