It's shareware, so there's some things we know.
There are people who are going to want to use your software, and are perfectly willing to pay for it. All you have to do for them is get them to try out your software, and don't make it hard to pay. (For me, Paypal is quick and easy, but mailing a check becomes a chore.)
There are people who just aren't going to pay for your software, and what they do doesn't affect you. You're probably actually a little better off if they cheat; that way, they might interest somebody who might pay you. Try to stop them from using your software if you like, but don't kid yourself into thinking this will get you a dime more.
There are people who are willing to pay you, but would prefer to use it for free. These people are who you want to worry about. You want to make it less of a problem to just pay you than to cheat. If the cost is reasonable, they aren't going to put an unreasonable amount of effort into using it anyway, so you don't need to get into overly restrictive measures. (Remember that the only people who will work hard to cheat are the ones that wouldn't pay you in any case.)
Remember also that making the protection unduly annoying is going to move people from the "could pay" to "won't pay" categories. Many contemporary examples to the contrary, I really don't think that annoying your legitimate customers is a vital part of a business plan.
There's nothing you can do, short of phoning home enough to cause lots of other problems, to prevent everybody from cracking your protection scheme, so if it's worth selling on the first place somebody will crack it, and likely put it on Pirate Bay. Don't worry about that, since there's nothing much you can do about it. Save your effort for things that will give you more profit. EDIT: Be very careful about protecting your application. You do not want the Pirate Bay version to be clearly superior to the legitimate version. You also want legit customers saying "It's great, and no problem to install" rather than "It disabled my DVD drive and impregnated my gerbil, but after that it was great to have".
Finally, I don't see the difference between Windows and MacOSX here. If I download some shareware for Windows, I keep the .zip file around, and I can uninstall and reinstall, or reset the system date. For MacOS, i can uninstall and reinstall, or reset the system date, and Time Machine can automate some of this. What's the issue here? (Remember that if you leave uninstallable bits where they can cause problems later, you're potentially annoying the cash customers.)
My recommendation would be to not worry about it too much.