Some well known pros are claiming that the move from Aperture to Lightroom is "Fast, Fun and Easy." The tutorial takes TWO HOURS. And that's a tutorial. The uninitiated may find that it takes far more than that and if you make a mistake, well, that's not covered. Look it up if you feel adventurous, but I wouldn't recommend it except the most experienced of users.
There is also an automated application that I have not yet tried, called Aperture Exporter ($14.99, CHEAP if it works) - http://apertureexporter.com/ - according to their website, "Aperture Exporter was designed specifically for Aperture users who have decided to move to Lightroom. With only a few options and a click of a button, Aperture Exporter re-generates your Aperture Library as a set of folders and subfolders containing your images." I have not yet had the chance to try it. I will report back on it once I've had an opportunity to use it. Or, if you try it, please let me know how well it worked.
Moving from Aperture to Lightroom is a very big challenge. And, since Aperture does not catalog photos in a logical folder sequence that can simply be imported to Lightroom, I'd recommend getting an expert to help you or to give Aperture Exporter a try.
But whatever you do, DON'T move any of your files in the finder. You may find all your files are missing! You can move them later from within Lightroom, once you've successfully imported your Aperture library.