Well, you certainly won't find a shortage of opinions on Slashdot. :-)
If you think the software is good enough, then a non-commercial version with limited registration information (e-mail, name), and some very privacy-thoughtful reporting (maybe to ensure that the registered serial numbers are only being used by one machine at a time), should only be a good thing. Getting your software into the hands of the people that might buy it will get them used to it, relying on it, and eventually make them customers. But (as others here have posted), don't abuse the "spying"... if you start to make money by pilfering the free registrations for ancillary information you're just going to annoy your users and they'll be more apt to pirate the software or use fake registration information. Giving them something in return, like forum access for very limited support, is helpful.
Other possible models include giving the software for free and asking payment for support -- nearly all profitable Open Source companies do this, and even if you leave the source closed the business model isn't terribly different. You could publish a "crippleware" version, which I find rather annoying, unless the limits are such that the home and non-commercial users needs are really satisfied, and the only people that need to pay $10k for the software are those to whom it's worth it. I give a nice shout out to Andrea Mosaic for doing this correctly (at a lower price point).
Lastly an option you may have missed may be to ignore it because it isn't a problem. A pirated version by a customer that wouldn't have paid anyway probably doesn't hurt you. A pirated version by a customer that would have paid may actually turn into a sale if they need assistance. When you upgrade, if the pirates liked it, they'll want the next version, so they may buy. It may be pirated by employees or students who years later may remember it and decide to buy it. You never can tell.
In those cases, you're getting your software out there and used; you could take an "all exposure is good exposure" attitude. The fact that you didn't list the name of your software in the original post here means that you may not think that way, or you may outright disagree.
Still, piracy is going to happen. At least you're asking the right questions. Don't let yourself get dragged into a fight with the anonymous masses on the internet, though -- you'll probably lose.