I've been using Lightkey 3-4 times a week for a bit over a year. It has grown to be very stable in my environment, and is very intuitive if you think ahead when setting up your presets (as with any DMX software, it's as easy or as difficult as your preparation makes it).
The MacUpdate page and previous comments are misleading on the price—there is a free mode, with all the features, the only limitation is it only works for 24 channels. No payment required. Then there are the different tiers of pricing which unlock additional DMX channels. Most people would probably go for the 512 which is $99 a year currently.
I would recommend this software to anyone where you need it to be simple and obvious for your operators. If you're a real LD, sure, go get a PC and run M-PC for free... but LightKey is filling a wide gap of user-friendly, intuitive, Mac-native, DMX software.
The fact that it works with so many interfaces and is regularly updated is a huge bonus.
I currently use a DMX King USB interface and have the 512 license. Would recommend.
If I could make any suggestion to the devs, it would be that an ability to OFFSET the HOME Pan/Tilt of fixtures by ±180 degrees would be amazing. And an ability to MIRROR the PAN and/or TILT of a fixture would be amazing. Both in the actual DMX values, and in the live preview.
Reason being, one venue I run shows has mounted their fixtures in directions that don't quite make sense and aren't consistent. So If I give 4 lights on a back truss a position of 0°/90° (p/t), 3 of them shoot straight out, and one of them shoots to the side. I want to offset that light be 90° pan, so it will be more properly in sync. I understand this is a band-aid to correcting the actualy physical position, but it's not my venue to go up and move fixtures.