As you've probably heard by now, Apple has announced plans to ditch DRM for good. That means all songs you purchase from iTunes will arrive on your PC without the usual copy-protection shackles.
However, this doesn't give you carte blanche. Because Apple still encodes songs using the proprietary AAC format, your downloads won't play in many phones, PDAs, MP3 players and so on. They will, of course, play on your Apple iPod or iPhone.
Fortunately, it's fairly easy to convert iTunes Plus purchases (ie, the DRM-free versions of songs) to the universally compatible MP3 format.
In iTunes, go to Edit, Preferences, General. Click the Import Settings button. Change the Import Using option to MP3 Encoder. In the Setting field, choose Custom, and then set Stereo Bit Rate to your desired setting (I recommend 256Kbit/sec. or 320Kbit/sec.). Click OK three times to exit the various windows.
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Now, you're all set to convert any iTunes Plus download to the MP3 format. To do that, right-click the song and choose Create MP3 Version. Wait a minute or so and presto: iTunes plops an MP3 copy of the song into your library.
Note that you'll now have both versions of the song in your library, so you'll have to do a little housekeeping.
The bigger downside is that converting from AAC to MP3 necessarily involves some loss of audio fidelity. Not much, but if you're a purist, you may want to skip iTunes altogether and buy MP3s outright from a store like AmazonMP3.