Tax Cut includes standard features that you'd expect from a tax preparation program, such as the ability to import data from Quicken, TurboTax, or TaxCut in windows or mac flavors. In addition, the premium edition includes one free question to a tax advisor. Of course, all data is encrypted via 128-bit AES.
H&R block has included several mac-specific features in this year's version to sweeten the deal, including the ability to import address book information, iDisk backup or restore from another user's iDisk, and subscribing to iCal calendars with tax related dates (filing deadlines, etc).
TaxCut starts at $19.99 for the Federal version, $39.99 for the Federal+State edition, and $69.99 for the Federal+State+e-file edition.