Hi,
I’ve also downloaded the free, non-commercial version.
And being a free program, it’s incredible! If you want to know what it’s capable of, download some of the example AVI’s on the official homepage.
Limitations? TONS! But most of these are solved by YOU, when shooting the footage to be tracked.
Like most other tracking packages, Icarus works like a charm in a simple move forward/backward shot, with lots of markers on floor & walls. I tried it on a greenscreen crane shot of some Swedish pop music chicks, I downloaded from some VFX company’s homepage, and it worked great.
Then I tried it on some of my own handheld footage for a private CG project, and that worked like crap…
A piece of advice when shooting:
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Like I said, have lots of camera markers, kept in planes that’ll give a lot of information about camera position, like the floor and walls on the left and right.
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Have lots of the markers organized in vertical and horizontal lines, and on the floor, in a grid. - that’ll help you orient things in your 3D package.
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Keep the markers in places where they’ll be easy to remove digitally, though…
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Measure up the distance between the markers, in several places, if not all. That’ll help you scale things, of course…
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The longer time the markers stay in frame, the better. Markers leaving and entering the frame at will is NOT good.
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Want to track a CG object in on the floor or on the wall? Have a marker RIGHT THERE! Camera tracking is rarely an excact science, so don’t count on markers in the corners of a wall keeping perfect track of the middle of the wall! Things will slide…
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In addition to tracking not being exact science, don’t count on rebuilding your entire set digitally, based only on tracking data… that was our mistake! 
Apart from that, there are also some annoying “features” in the interface… I found the scale and orientation features to work in bizarre, random ways… :surprised
Also, twice I’ve experienced that trying to calculate a camera move based on too few tracking points, crashes the program and corrupts the file!! Yup, all tracking data lost. So save often, under different file names! 
But, all bugs aside, like I said, for a free program, it’s incredible… and if you shoot your footage well, Icarus can do wonderful things for you.
Cheers,
(I’ve tried it with Max & Maya, but not with Lightwave…)