There are a lot of complexities, to be sure. I just ran a test conversion on the entire library.
First thoughts? We've been blessed with Aperture these many years. Lightroom certainly has some capabilities when it comes to photo editing, but I can see why so many professionals have held out so long with Aperture. There just isn't a better personal-level DAM. I've been reading a book on Lightroom, and there are several limitations as far as manipulating and cataloging. Definitely some neat features as well, but for the most part, not as versatile as Aperture. I'm going to miss that.
I don't like the folder/collections paradigm. Feel like I'm in a straight jacket. But at least it gives me some versatility. Based on testing, I figure I'll reference my masters as year/project, to provide some organization. More than that, it gets difficult to move around within the browser pane.
The plugin has it's problems, but it did perform better than expectations. Out of 40,000 photos, it managed to import all but 200 or so. Oddly, many groupings the same Aperture project. It did a good job of stacking images, but you don't see stacks in collections! It also did find and migrate a bunch of duplicate JPEG "masters" that were presumably created as I've exported to Facebook and other projects.
One gotcha, you should create full-sized previews if you want those migrated, too.
The faces tagging doesn't work yet. And much of my keywords were scrambled. Certainly can pick up the pieces, but that endeavor will take several hours as well. Lightroom won't make this very easy. It seems a bit more cumbersome to navigate, filter, and sort, but perhaps that's just due to my lack of experience.
I only have 1400 stacks, so I figure I'll create a metadata reference for the "pick", flag them in Lightroom, then go through stacks one by one and restack them. Shouldn't take more than a half a day.
Adobe support and forums just aren't very good. Few people participate, even though there is a larger Lightroom community??