>> I have not tried it, but watched a few of their videos (which show that there are lots of sliders, but offer only a poor indication of what they do).
You need to experiment IMHO - I didn't get the manual for it until I'd done a lot of testing ;-) Download the demo - the manual has descriptions of many of the functions. Personally I don't find videos of any real help, but I appreciate that YMMV ;-)
>> Having sooo many sliders seems to be overkill, but they do have presets that give you an indication of what you can expect, and you can apply the looks selectively (eg, sky v foreground) so it may work OK in practice.
Definitely not overkill from my POV - add them to the layering/masking capabilities and it makes for a powerful combination. All the presets do help though ;-)
>> What the videos don't show is how much extra noise you get from processing.
Very little if the original images are good quality. I did notice that de-ghosting produced noisier shadows in the boat example in my review, but they were hardly an optimal source image set ;-)
>> It would be good to get an overview of the strengths and weaknesses of the main contenders (Macphun, Topaz Labs, Nik Software, On One, versus Lightroom / ACR) not just for HDR, but the full range of effects.
I have reviews of the Nik software on the Northlight site, but I'm afraid comparative reviews like you suggest need an awful lot of work if they are to be meaningful ;-)