I can't use files that I unzip on my Mac

To solve this, simply choose File->Preferences->Miscellaneous (or Edit->Preferences-> Miscellaneous in ZipIt 2.0) and uncheck "Smart-strip linefeeds from text files." Then, close any open ZipIt windows, open the zip archive and proceed.

After you unzip the file, you may need to start the application that you intend to use, choose open from the File menu, and select the file you just unzipped. That is, you may not be able to simply double-click the file to open it.