Rental periods mean DRM, and BitTorrent has chosen to go with Windows Media Player, so purchased content will only be usable on Windows PCs and devices compatible with protected WMV files.

So don't rent a movie from BitTorrent if you were planning to watch it on your iPod during your long train commute or on that two-hour flight you're taking tomorrow. Presumably people in that situation will continue to rip purchased DVDs or download unauthorised copies using BitTorrent.

Some people complain that content purchased from Apple's iTunes Store can only be played on iPods, overlooking the fact that it can also be played on personal computers running Windows or Mac OS X. The file format chosen by BitTorrent can be used by owners of portable devices that have licensed Microsoft's DRM technology, but not on computers running Mac OS X or Linux.