You might be familiar with Amazon.com's "Customers also bought..." feature; the iTunes MiniStore fills the same role in iTunes, and is a godsend for helping you find music matching your taste (in most cases).
iTunes MiniStore is visible by default, but might not have been turned on, or might have been turned off. Here is the MiniStore as it appears until you make your fateful choice:
Click Turn on MiniStore to start using it; if the MiniStore is not visible, choose Show MiniStore from iTunes' View menu. The MiniStore can only be turned on if iTunes is currently showing one of the following sections: Music, Movies, TV Shows, Audiobooks, Purchased, or a playlist/smart playlist. (Just click on any of these if needed.)
Keyboard shortcut: to show or hide iTunes' MiniStore, press Ctrl+Shift+M (Windows) or Command+Shift+M (Mac)
To hide the iTunes MiniStore, simply repeat the same procedure, and the MiniStore will slide into invisibility!
iTunes' MiniStore updates its content "contextually", when you click on an item: the content does not change when iTunes automatically plays the next item in the current list.
The MiniStore is divided in three sections. "Inside the Store" displays tools related to the last song you clicked on: you can read customer reviews, email a link to this song in the iTunes store to a friend, etc. The section "More from [Artist Name]" displays other works from the same artist; this lets you quickly check if the iTunes store added more content from your favorite artists.
The final section, "Listeners Also Bought", may be the most addictive and useful feature: it displays songs purchased by customers who purchased the song you just clicked on. This feature often lets you discover similar artists you may otherwise never have come across. Since the feature is based on purchases, and not an actual analysis of style, rhythm, etc. you might end up with a few disappointing results, since many customers will have eclectic tastes.
The "Concert Tickets", available only for some artists, opens a browser window to TicketMaster.com, showing the artist in question, and enabling you to search for future concerts in your area.
Until recently, music sold through iTunes' online store was copy-protected, and contained DRM (Digital Right Managements) software limiting the options with music you purchased. (Copy-protected music cannot be transferred onto any MP3 player, for example, whereas DRM-free MP3 files can play on iPods, Zunes, Creative Zens…)
Recent social trends are pushing distribution companies towards unprotected music downloads. A quick way to determine if a particular piece of music in iTunes is DRM-free: click on the song, and look at the MiniStore summary. If the mention "iTunes Plus" appears, your music is DRM-free (and truly yours).
Non iTunes Plus tracks are encoded with 128 kilobits per second (kbps), while iTunes Plus tracks use 256 kbps: these files have a higher sound quality, although the difference is inaudible to many people. For most, the main attraction of iTunes Plus files is the fact that they can be used without restriction, since they are DRM-free.
You can upgrade your iTunes library (link will open in iTunes).